linux/Documentation/sysctl/kernel.txt

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Documentation for /proc/sys/kernel/* kernel version 2.2.10
(c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
documentation: update Documentation/filesystem/proc.txt and Documentation/sysctls Now /proc/sys is described in many places and much information is redundant. This patch updates the proc.txt and move the /proc/sys desciption out to the files in Documentation/sysctls. Details are: merge - 2.1 /proc/sys/fs - File system data - 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem - 2.17 /proc/sys/fs/epoll - Configuration options for the epoll interface with Documentation/sysctls/fs.txt. remove - 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats since it's not better then the Documentation/binfmt_misc.txt. merge - 2.3 /proc/sys/kernel - general kernel parameters with Documentation/sysctls/kernel.txt remove - 2.5 /proc/sys/dev - Device specific parameters since it's obsolete the sysfs is used now. remove - 2.6 /proc/sys/sunrpc - Remote procedure calls since it's not better then the Documentation/sysctls/sunrpc.txt move - 2.7 /proc/sys/net - Networking stuff - 2.9 Appletalk - 2.10 IPX to newly created Documentation/sysctls/net.txt. remove - 2.8 /proc/sys/net/ipv4 - IPV4 settings since it's not better then the Documentation/networking/ip-sysctl.txt. add - Chapter 3 Per-Process Parameters to descibe /proc/<pid>/xxx parameters. Signed-off-by: Shen Feng <shen@cn.fujitsu.com> Cc: Randy Dunlap <randy.dunlap@oracle.com> Cc: "David S. Miller" <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-03 07:57:20 +08:00
(c) 2009, Shen Feng<shen@cn.fujitsu.com>
For general info and legal blurb, please look in README.
==============================================================
This file contains documentation for the sysctl files in
/proc/sys/kernel/ and is valid for Linux kernel version 2.2.
The files in this directory can be used to tune and monitor
miscellaneous and general things in the operation of the Linux
kernel. Since some of the files _can_ be used to screw up your
system, it is advisable to read both documentation and source
before actually making adjustments.
Currently, these files might (depending on your configuration)
show up in /proc/sys/kernel:
- acct
- acpi_video_flags
- auto_msgmni
- bootloader_type [ X86 only ]
- bootloader_version [ X86 only ]
- callhome [ S390 only ]
- cap_last_cap
- core_pattern
- core_pipe_limit
- core_uses_pid
- ctrl-alt-del
- dmesg_restrict
- domainname
- hostname
- hotplug
- hung_task_panic
- hung_task_check_count
- hung_task_timeout_secs
- hung_task_warnings
kexec: add sysctl to disable kexec_load For general-purpose (i.e. distro) kernel builds it makes sense to build with CONFIG_KEXEC to allow end users to choose what kind of things they want to do with kexec. However, in the face of trying to lock down a system with such a kernel, there needs to be a way to disable kexec_load (much like module loading can be disabled). Without this, it is too easy for the root user to modify kernel memory even when CONFIG_STRICT_DEVMEM and modules_disabled are set. With this change, it is still possible to load an image for use later, then disable kexec_load so the image (or lack of image) can't be altered. The intention is for using this in environments where "perfect" enforcement is hard. Without a verified boot, along with verified modules, and along with verified kexec, this is trying to give a system a better chance to defend itself (or at least grow the window of discoverability) against attack in the face of a privilege escalation. In my mind, I consider several boot scenarios: 1) Verified boot of read-only verified root fs loading fd-based verification of kexec images. 2) Secure boot of writable root fs loading signed kexec images. 3) Regular boot loading kexec (e.g. kcrash) image early and locking it. 4) Regular boot with no control of kexec image at all. 1 and 2 don't exist yet, but will soon once the verified kexec series has landed. 4 is the state of things now. The gap between 2 and 4 is too large, so this change creates scenario 3, a middle-ground above 4 when 2 and 1 are not possible for a system. Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: Rik van Riel <riel@redhat.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Eric Biederman <ebiederm@xmission.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-01-24 07:55:59 +08:00
- kexec_load_disabled
kptr_restrict for hiding kernel pointers from unprivileged users Add the %pK printk format specifier and the /proc/sys/kernel/kptr_restrict sysctl. The %pK format specifier is designed to hide exposed kernel pointers, specifically via /proc interfaces. Exposing these pointers provides an easy target for kernel write vulnerabilities, since they reveal the locations of writable structures containing easily triggerable function pointers. The behavior of %pK depends on the kptr_restrict sysctl. If kptr_restrict is set to 0, no deviation from the standard %p behavior occurs. If kptr_restrict is set to 1, the default, if the current user (intended to be a reader via seq_printf(), etc.) does not have CAP_SYSLOG (currently in the LSM tree), kernel pointers using %pK are printed as 0's. If kptr_restrict is set to 2, kernel pointers using %pK are printed as 0's regardless of privileges. Replacing with 0's was chosen over the default "(null)", which cannot be parsed by userland %p, which expects "(nil)". [akpm@linux-foundation.org: check for IRQ context when !kptr_restrict, save an indent level, s/WARN/WARN_ONCE/] [akpm@linux-foundation.org: coding-style fixup] [randy.dunlap@oracle.com: fix kernel/sysctl.c warning] Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com> Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: James Morris <jmorris@namei.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Thomas Graf <tgraf@infradead.org> Cc: Eugene Teo <eugeneteo@kernel.org> Cc: Kees Cook <kees.cook@canonical.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: David S. Miller <davem@davemloft.net> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Eric Paris <eparis@parisplace.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-01-13 08:59:41 +08:00
- kptr_restrict
- kstack_depth_to_print [ X86 only ]
- l2cr [ PPC only ]
- modprobe ==> Documentation/debugging-modules.txt
- modules_disabled
- msg_next_id [ sysv ipc ]
- msgmax
- msgmnb
- msgmni
documentation: update Documentation/filesystem/proc.txt and Documentation/sysctls Now /proc/sys is described in many places and much information is redundant. This patch updates the proc.txt and move the /proc/sys desciption out to the files in Documentation/sysctls. Details are: merge - 2.1 /proc/sys/fs - File system data - 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem - 2.17 /proc/sys/fs/epoll - Configuration options for the epoll interface with Documentation/sysctls/fs.txt. remove - 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats since it's not better then the Documentation/binfmt_misc.txt. merge - 2.3 /proc/sys/kernel - general kernel parameters with Documentation/sysctls/kernel.txt remove - 2.5 /proc/sys/dev - Device specific parameters since it's obsolete the sysfs is used now. remove - 2.6 /proc/sys/sunrpc - Remote procedure calls since it's not better then the Documentation/sysctls/sunrpc.txt move - 2.7 /proc/sys/net - Networking stuff - 2.9 Appletalk - 2.10 IPX to newly created Documentation/sysctls/net.txt. remove - 2.8 /proc/sys/net/ipv4 - IPV4 settings since it's not better then the Documentation/networking/ip-sysctl.txt. add - Chapter 3 Per-Process Parameters to descibe /proc/<pid>/xxx parameters. Signed-off-by: Shen Feng <shen@cn.fujitsu.com> Cc: Randy Dunlap <randy.dunlap@oracle.com> Cc: "David S. Miller" <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-03 07:57:20 +08:00
- nmi_watchdog
- osrelease
- ostype
- overflowgid
- overflowuid
- panic
- panic_on_oops
- panic_on_stackoverflow
kernel: add panic_on_warn There have been several times where I have had to rebuild a kernel to cause a panic when hitting a WARN() in the code in order to get a crash dump from a system. Sometimes this is easy to do, other times (such as in the case of a remote admin) it is not trivial to send new images to the user. A much easier method would be a switch to change the WARN() over to a panic. This makes debugging easier in that I can now test the actual image the WARN() was seen on and I do not have to engage in remote debugging. This patch adds a panic_on_warn kernel parameter and /proc/sys/kernel/panic_on_warn calls panic() in the warn_slowpath_common() path. The function will still print out the location of the warning. An example of the panic_on_warn output: The first line below is from the WARN_ON() to output the WARN_ON()'s location. After that the panic() output is displayed. WARNING: CPU: 30 PID: 11698 at /home/prarit/dummy_module/dummy-module.c:25 init_dummy+0x1f/0x30 [dummy_module]() Kernel panic - not syncing: panic_on_warn set ... CPU: 30 PID: 11698 Comm: insmod Tainted: G W OE 3.17.0+ #57 Hardware name: Intel Corporation S2600CP/S2600CP, BIOS RMLSDP.86I.00.29.D696.1311111329 11/11/2013 0000000000000000 000000008e3f87df ffff88080f093c38 ffffffff81665190 0000000000000000 ffffffff818aea3d ffff88080f093cb8 ffffffff8165e2ec ffffffff00000008 ffff88080f093cc8 ffff88080f093c68 000000008e3f87df Call Trace: [<ffffffff81665190>] dump_stack+0x46/0x58 [<ffffffff8165e2ec>] panic+0xd0/0x204 [<ffffffffa038e05f>] ? init_dummy+0x1f/0x30 [dummy_module] [<ffffffff81076b90>] warn_slowpath_common+0xd0/0xd0 [<ffffffffa038e040>] ? dummy_greetings+0x40/0x40 [dummy_module] [<ffffffff81076c8a>] warn_slowpath_null+0x1a/0x20 [<ffffffffa038e05f>] init_dummy+0x1f/0x30 [dummy_module] [<ffffffff81002144>] do_one_initcall+0xd4/0x210 [<ffffffff811b52c2>] ? __vunmap+0xc2/0x110 [<ffffffff810f8889>] load_module+0x16a9/0x1b30 [<ffffffff810f3d30>] ? store_uevent+0x70/0x70 [<ffffffff810f49b9>] ? copy_module_from_fd.isra.44+0x129/0x180 [<ffffffff810f8ec6>] SyS_finit_module+0xa6/0xd0 [<ffffffff8166cf29>] system_call_fastpath+0x12/0x17 Successfully tested by me. hpa said: There is another very valid use for this: many operators would rather a machine shuts down than being potentially compromised either functionally or security-wise. Signed-off-by: Prarit Bhargava <prarit@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Acked-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> Cc: Fabian Frederick <fabf@skynet.be> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-12-11 07:45:50 +08:00
- panic_on_unrecovered_nmi
- panic_on_warn
- pid_max
- powersave-nap [ PPC only ]
- printk
- printk_delay
- printk_ratelimit
- printk_ratelimit_burst
- randomize_va_space
- real-root-dev ==> Documentation/initrd.txt
- reboot-cmd [ SPARC only ]
- rtsig-max
- rtsig-nr
- sem
- sem_next_id [ sysv ipc ]
- sg-big-buff [ generic SCSI device (sg) ]
- shm_next_id [ sysv ipc ]
ipc: introduce shm_rmid_forced sysctl Add support for the shm_rmid_forced sysctl. If set to 1, all shared memory objects in current ipc namespace will be automatically forced to use IPC_RMID. The POSIX way of handling shmem allows one to create shm objects and call shmdt(), leaving shm object associated with no process, thus consuming memory not counted via rlimits. With shm_rmid_forced=1 the shared memory object is counted at least for one process, so OOM killer may effectively kill the fat process holding the shared memory. It obviously breaks POSIX - some programs relying on the feature would stop working. So set shm_rmid_forced=1 only if you're sure nobody uses "orphaned" memory. Use shm_rmid_forced=0 by default for compatability reasons. The feature was previously impemented in -ow as a configure option. [akpm@linux-foundation.org: fix documentation, per Randy] [akpm@linux-foundation.org: fix warning] [akpm@linux-foundation.org: readability/conventionality tweaks] [akpm@linux-foundation.org: fix shm_rmid_forced/shm_forced_rmid confusion, use standard comment layout] Signed-off-by: Vasiliy Kulikov <segoon@openwall.com> Cc: Randy Dunlap <rdunlap@xenotime.net> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: "Serge E. Hallyn" <serge.hallyn@canonical.com> Cc: Daniel Lezcano <daniel.lezcano@free.fr> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Tejun Heo <tj@kernel.org> Cc: Ingo Molnar <mingo@elte.hu> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Solar Designer <solar@openwall.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-07-27 07:08:48 +08:00
- shm_rmid_forced
- shmall
- shmmax [ sysv ipc ]
- shmmni
kernel/watchdog.c: print traces for all cpus on lockup detection A 'softlockup' is defined as a bug that causes the kernel to loop in kernel mode for more than a predefined period to time, without giving other tasks a chance to run. Currently, upon detection of this condition by the per-cpu watchdog task, debug information (including a stack trace) is sent to the system log. On some occasions, we have observed that the "victim" rather than the actual "culprit" (i.e. the owner/holder of the contended resource) is reported to the user. Often this information has proven to be insufficient to assist debugging efforts. To avoid loss of useful debug information, for architectures which support NMI, this patch makes it possible to improve soft lockup reporting. This is accomplished by issuing an NMI to each cpu to obtain a stack trace. If NMI is not supported we just revert back to the old method. A sysctl and boot-time parameter is available to toggle this feature. [dzickus@redhat.com: add CONFIG_SMP in certain areas] [akpm@linux-foundation.org: additional CONFIG_SMP=n optimisations] [mq@suse.cz: fix warning] Signed-off-by: Aaron Tomlin <atomlin@redhat.com> Signed-off-by: Don Zickus <dzickus@redhat.com> Cc: David S. Miller <davem@davemloft.net> Cc: Mateusz Guzik <mguzik@redhat.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Jan Moskyto Matejka <mq@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-24 04:22:05 +08:00
- softlockup_all_cpu_backtrace
- stop-a [ SPARC only ]
- sysrq ==> Documentation/sysrq.txt
sysctl: allow for strict write position handling When writing to a sysctl string, each write, regardless of VFS position, begins writing the string from the start. This means the contents of the last write to the sysctl controls the string contents instead of the first: open("/proc/sys/kernel/modprobe", O_WRONLY) = 1 write(1, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 4096) = 4096 write(1, "/bin/true", 9) = 9 close(1) = 0 $ cat /proc/sys/kernel/modprobe /bin/true Expected behaviour would be to have the sysctl be "AAAA..." capped at maxlen (in this case KMOD_PATH_LEN: 256), instead of truncating to the contents of the second write. Similarly, multiple short writes would not append to the sysctl. The old behavior is unlike regular POSIX files enough that doing audits of software that interact with sysctls can end up in unexpected or dangerous situations. For example, "as long as the input starts with a trusted path" turns out to be an insufficient filter, as what must also happen is for the input to be entirely contained in a single write syscall -- not a common consideration, especially for high level tools. This provides kernel.sysctl_writes_strict as a way to make this behavior act in a less surprising manner for strings, and disallows non-zero file position when writing numeric sysctls (similar to what is already done when reading from non-zero file positions). For now, the default (0) is to warn about non-zero file position use, but retain the legacy behavior. Setting this to -1 disables the warning, and setting this to 1 enables the file position respecting behavior. [akpm@linux-foundation.org: fix build] [akpm@linux-foundation.org: move misplaced hunk, per Randy] Signed-off-by: Kees Cook <keescook@chromium.org> Cc: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-07 05:37:19 +08:00
- sysctl_writes_strict
- tainted
- threads-max
documentation: update Documentation/filesystem/proc.txt and Documentation/sysctls Now /proc/sys is described in many places and much information is redundant. This patch updates the proc.txt and move the /proc/sys desciption out to the files in Documentation/sysctls. Details are: merge - 2.1 /proc/sys/fs - File system data - 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem - 2.17 /proc/sys/fs/epoll - Configuration options for the epoll interface with Documentation/sysctls/fs.txt. remove - 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats since it's not better then the Documentation/binfmt_misc.txt. merge - 2.3 /proc/sys/kernel - general kernel parameters with Documentation/sysctls/kernel.txt remove - 2.5 /proc/sys/dev - Device specific parameters since it's obsolete the sysfs is used now. remove - 2.6 /proc/sys/sunrpc - Remote procedure calls since it's not better then the Documentation/sysctls/sunrpc.txt move - 2.7 /proc/sys/net - Networking stuff - 2.9 Appletalk - 2.10 IPX to newly created Documentation/sysctls/net.txt. remove - 2.8 /proc/sys/net/ipv4 - IPV4 settings since it's not better then the Documentation/networking/ip-sysctl.txt. add - Chapter 3 Per-Process Parameters to descibe /proc/<pid>/xxx parameters. Signed-off-by: Shen Feng <shen@cn.fujitsu.com> Cc: Randy Dunlap <randy.dunlap@oracle.com> Cc: "David S. Miller" <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-03 07:57:20 +08:00
- unknown_nmi_panic
- watchdog_thresh
- version
==============================================================
acct:
highwater lowwater frequency
If BSD-style process accounting is enabled these values control
its behaviour. If free space on filesystem where the log lives
goes below <lowwater>% accounting suspends. If free space gets
above <highwater>% accounting resumes. <Frequency> determines
how often do we check the amount of free space (value is in
seconds). Default:
4 2 30
That is, suspend accounting if there left <= 2% free; resume it
if we got >=4%; consider information about amount of free space
valid for 30 seconds.
==============================================================
acpi_video_flags:
flags
See Doc*/kernel/power/video.txt, it allows mode of video boot to be
set during run time.
==============================================================
auto_msgmni:
This variable has no effect and may be removed in future kernel
releases. Reading it always returns 0.
Up to Linux 3.17, it enabled/disabled automatic recomputing of msgmni
upon memory add/remove or upon ipc namespace creation/removal.
Echoing "1" into this file enabled msgmni automatic recomputing.
Echoing "0" turned it off. auto_msgmni default value was 1.
==============================================================
bootloader_type:
x86 bootloader identification
This gives the bootloader type number as indicated by the bootloader,
shifted left by 4, and OR'd with the low four bits of the bootloader
version. The reason for this encoding is that this used to match the
type_of_loader field in the kernel header; the encoding is kept for
backwards compatibility. That is, if the full bootloader type number
is 0x15 and the full version number is 0x234, this file will contain
the value 340 = 0x154.
See the type_of_loader and ext_loader_type fields in
Documentation/x86/boot.txt for additional information.
==============================================================
bootloader_version:
x86 bootloader version
The complete bootloader version number. In the example above, this
file will contain the value 564 = 0x234.
See the type_of_loader and ext_loader_ver fields in
Documentation/x86/boot.txt for additional information.
==============================================================
callhome:
Controls the kernel's callhome behavior in case of a kernel panic.
The s390 hardware allows an operating system to send a notification
to a service organization (callhome) in case of an operating system panic.
When the value in this file is 0 (which is the default behavior)
nothing happens in case of a kernel panic. If this value is set to "1"
the complete kernel oops message is send to the IBM customer service
organization in case the mainframe the Linux operating system is running
on has a service contract with IBM.
==============================================================
cap_last_cap
Highest valid capability of the running kernel. Exports
CAP_LAST_CAP from the kernel.
==============================================================
core_pattern:
core_pattern is used to specify a core dumpfile pattern name.
. max length 128 characters; default value is "core"
. core_pattern is used as a pattern template for the output filename;
certain string patterns (beginning with '%') are substituted with
their actual values.
. backward compatibility with core_uses_pid:
If core_pattern does not include "%p" (default does not)
and core_uses_pid is set, then .PID will be appended to
the filename.
. corename format specifiers:
%<NUL> '%' is dropped
%% output one '%'
%p pid
%P global pid (init PID namespace)
coredump: add %i/%I in core_pattern to report the tid of the crashed thread format_corename() can only pass the leader's pid to the core handler, but there is no simple way to figure out which thread originated the coredump. As Jan explains, this also means that there is no simple way to create the backtrace of the crashed process: As programs are mostly compiled with implicit gcc -fomit-frame-pointer one needs program's .eh_frame section (equivalently PT_GNU_EH_FRAME segment) or .debug_frame section. .debug_frame usually is present only in separate debug info files usually not even installed on the system. While .eh_frame is a part of the executable/library (and it is even always mapped for C++ exceptions unwinding) it no longer has to be present anywhere on the disk as the program could be upgraded in the meantime and the running instance has its executable file already unlinked from disk. One possibility is to echo 0x3f >/proc/*/coredump_filter and dump all the file-backed memory including the executable's .eh_frame section. But that can create huge core files, for example even due to mmapped data files. Other possibility would be to read .eh_frame from /proc/PID/mem at the core_pattern handler time of the core dump. For the backtrace one needs to read the register state first which can be done from core_pattern handler: ptrace(PTRACE_SEIZE, tid, 0, PTRACE_O_TRACEEXIT) close(0); // close pipe fd to resume the sleeping dumper waitpid(); // should report EXIT PTRACE_GETREGS or other requests The remaining problem is how to get the 'tid' value of the crashed thread. It could be read from the first NT_PRSTATUS note of the core file but that makes the core_pattern handler complicated. Unfortunately %t is already used so this patch uses %i/%I. Automatic Bug Reporting Tool (https://github.com/abrt/abrt/wiki/overview) is experimenting with this. It is using the elfutils (https://fedorahosted.org/elfutils/) unwinder for generating the backtraces. Apart from not needing matching executables as mentioned above, another advantage is that we can get the backtrace without saving the core (which might be quite large) to disk. [mmilata@redhat.com: final paragraph of changelog] Signed-off-by: Jan Kratochvil <jan.kratochvil@redhat.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Jan Kratochvil <jan.kratochvil@redhat.com> Cc: Mark Wielaard <mjw@redhat.com> Cc: Martin Milata <mmilata@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-14 06:53:35 +08:00
%i tid
%I global tid (init PID namespace)
%u uid
%g gid
%d dump mode, matches PR_SET_DUMPABLE and
/proc/sys/fs/suid_dumpable
%s signal number
%t UNIX time of dump
%h hostname
%e executable filename (may be shortened)
%E executable path
%<OTHER> both are dropped
. If the first character of the pattern is a '|', the kernel will treat
the rest of the pattern as a command to run. The core dump will be
written to the standard input of that program instead of to a file.
==============================================================
core_pipe_limit:
This sysctl is only applicable when core_pattern is configured to pipe
core files to a user space helper (when the first character of
core_pattern is a '|', see above). When collecting cores via a pipe
to an application, it is occasionally useful for the collecting
application to gather data about the crashing process from its
/proc/pid directory. In order to do this safely, the kernel must wait
for the collecting process to exit, so as not to remove the crashing
processes proc files prematurely. This in turn creates the
possibility that a misbehaving userspace collecting process can block
the reaping of a crashed process simply by never exiting. This sysctl
defends against that. It defines how many concurrent crashing
processes may be piped to user space applications in parallel. If
this value is exceeded, then those crashing processes above that value
are noted via the kernel log and their cores are skipped. 0 is a
special value, indicating that unlimited processes may be captured in
parallel, but that no waiting will take place (i.e. the collecting
process is not guaranteed access to /proc/<crashing pid>/). This
value defaults to 0.
==============================================================
core_uses_pid:
The default coredump filename is "core". By setting
core_uses_pid to 1, the coredump filename becomes core.PID.
If core_pattern does not include "%p" (default does not)
and core_uses_pid is set, then .PID will be appended to
the filename.
==============================================================
ctrl-alt-del:
When the value in this file is 0, ctrl-alt-del is trapped and
sent to the init(1) program to handle a graceful restart.
When, however, the value is > 0, Linux's reaction to a Vulcan
Nerve Pinch (tm) will be an immediate reboot, without even
syncing its dirty buffers.
Note: when a program (like dosemu) has the keyboard in 'raw'
mode, the ctrl-alt-del is intercepted by the program before it
ever reaches the kernel tty layer, and it's up to the program
to decide what to do with it.
==============================================================
dmesg_restrict:
This toggle indicates whether unprivileged users are prevented
from using dmesg(8) to view messages from the kernel's log buffer.
When dmesg_restrict is set to (0) there are no restrictions. When
dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use
dmesg(8).
The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the
default value of dmesg_restrict.
==============================================================
domainname & hostname:
These files can be used to set the NIS/YP domainname and the
hostname of your box in exactly the same way as the commands
domainname and hostname, i.e.:
# echo "darkstar" > /proc/sys/kernel/hostname
# echo "mydomain" > /proc/sys/kernel/domainname
has the same effect as
# hostname "darkstar"
# domainname "mydomain"
Note, however, that the classic darkstar.frop.org has the
hostname "darkstar" and DNS (Internet Domain Name Server)
domainname "frop.org", not to be confused with the NIS (Network
Information Service) or YP (Yellow Pages) domainname. These two
domain names are in general different. For a detailed discussion
see the hostname(1) man page.
==============================================================
hotplug:
Path for the hotplug policy agent.
Default value is "/sbin/hotplug".
==============================================================
hung_task_panic:
Controls the kernel's behavior when a hung task is detected.
This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
0: continue operation. This is the default behavior.
1: panic immediately.
==============================================================
hung_task_check_count:
The upper bound on the number of tasks that are checked.
This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
==============================================================
hung_task_timeout_secs:
Check interval. When a task in D state did not get scheduled
for more than this value report a warning.
This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
0: means infinite timeout - no checking done.
Possible values to set are in range {0..LONG_MAX/HZ}.
==============================================================
hung_task_warnings:
The maximum number of warnings to report. During a check interval
if a hung task is detected, this value is decreased by 1.
When this value reaches 0, no more warnings will be reported.
This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
-1: report an infinite number of warnings.
==============================================================
kexec: add sysctl to disable kexec_load For general-purpose (i.e. distro) kernel builds it makes sense to build with CONFIG_KEXEC to allow end users to choose what kind of things they want to do with kexec. However, in the face of trying to lock down a system with such a kernel, there needs to be a way to disable kexec_load (much like module loading can be disabled). Without this, it is too easy for the root user to modify kernel memory even when CONFIG_STRICT_DEVMEM and modules_disabled are set. With this change, it is still possible to load an image for use later, then disable kexec_load so the image (or lack of image) can't be altered. The intention is for using this in environments where "perfect" enforcement is hard. Without a verified boot, along with verified modules, and along with verified kexec, this is trying to give a system a better chance to defend itself (or at least grow the window of discoverability) against attack in the face of a privilege escalation. In my mind, I consider several boot scenarios: 1) Verified boot of read-only verified root fs loading fd-based verification of kexec images. 2) Secure boot of writable root fs loading signed kexec images. 3) Regular boot loading kexec (e.g. kcrash) image early and locking it. 4) Regular boot with no control of kexec image at all. 1 and 2 don't exist yet, but will soon once the verified kexec series has landed. 4 is the state of things now. The gap between 2 and 4 is too large, so this change creates scenario 3, a middle-ground above 4 when 2 and 1 are not possible for a system. Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: Rik van Riel <riel@redhat.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Eric Biederman <ebiederm@xmission.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-01-24 07:55:59 +08:00
kexec_load_disabled:
A toggle indicating if the kexec_load syscall has been disabled. This
value defaults to 0 (false: kexec_load enabled), but can be set to 1
(true: kexec_load disabled). Once true, kexec can no longer be used, and
the toggle cannot be set back to false. This allows a kexec image to be
loaded before disabling the syscall, allowing a system to set up (and
later use) an image without it being altered. Generally used together
with the "modules_disabled" sysctl.
==============================================================
kptr_restrict for hiding kernel pointers from unprivileged users Add the %pK printk format specifier and the /proc/sys/kernel/kptr_restrict sysctl. The %pK format specifier is designed to hide exposed kernel pointers, specifically via /proc interfaces. Exposing these pointers provides an easy target for kernel write vulnerabilities, since they reveal the locations of writable structures containing easily triggerable function pointers. The behavior of %pK depends on the kptr_restrict sysctl. If kptr_restrict is set to 0, no deviation from the standard %p behavior occurs. If kptr_restrict is set to 1, the default, if the current user (intended to be a reader via seq_printf(), etc.) does not have CAP_SYSLOG (currently in the LSM tree), kernel pointers using %pK are printed as 0's. If kptr_restrict is set to 2, kernel pointers using %pK are printed as 0's regardless of privileges. Replacing with 0's was chosen over the default "(null)", which cannot be parsed by userland %p, which expects "(nil)". [akpm@linux-foundation.org: check for IRQ context when !kptr_restrict, save an indent level, s/WARN/WARN_ONCE/] [akpm@linux-foundation.org: coding-style fixup] [randy.dunlap@oracle.com: fix kernel/sysctl.c warning] Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com> Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: James Morris <jmorris@namei.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Thomas Graf <tgraf@infradead.org> Cc: Eugene Teo <eugeneteo@kernel.org> Cc: Kees Cook <kees.cook@canonical.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: David S. Miller <davem@davemloft.net> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Eric Paris <eparis@parisplace.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-01-13 08:59:41 +08:00
kptr_restrict:
This toggle indicates whether restrictions are placed on
vsprintf: check real user/group id for %pK Some setuid binaries will allow reading of files which have read permission by the real user id. This is problematic with files which use %pK because the file access permission is checked at open() time, but the kptr_restrict setting is checked at read() time. If a setuid binary opens a %pK file as an unprivileged user, and then elevates permissions before reading the file, then kernel pointer values may be leaked. This happens for example with the setuid pppd application on Ubuntu 12.04: $ head -1 /proc/kallsyms 00000000 T startup_32 $ pppd file /proc/kallsyms pppd: In file /proc/kallsyms: unrecognized option 'c1000000' This will only leak the pointer value from the first line, but other setuid binaries may leak more information. Fix this by adding a check that in addition to the current process having CAP_SYSLOG, that effective user and group ids are equal to the real ids. If a setuid binary reads the contents of a file which uses %pK then the pointer values will be printed as NULL if the real user is unprivileged. Update the sysctl documentation to reflect the changes, and also correct the documentation to state the kptr_restrict=0 is the default. This is a only temporary solution to the issue. The correct solution is to do the permission check at open() time on files, and to replace %pK with a function which checks the open() time permission. %pK uses in printk should be removed since no sane permission check can be done, and instead protected by using dmesg_restrict. Signed-off-by: Ryan Mallon <rmallon@gmail.com> Cc: Kees Cook <keescook@chromium.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Joe Perches <joe@perches.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-11-13 07:08:51 +08:00
exposing kernel addresses via /proc and other interfaces.
When kptr_restrict is set to (0), the default, there are no restrictions.
When kptr_restrict is set to (1), kernel pointers printed using the %pK
format specifier will be replaced with 0's unless the user has CAP_SYSLOG
and effective user and group ids are equal to the real ids. This is
because %pK checks are done at read() time rather than open() time, so
if permissions are elevated between the open() and the read() (e.g via
a setuid binary) then %pK will not leak kernel pointers to unprivileged
users. Note, this is a temporary solution only. The correct long-term
solution is to do the permission checks at open() time. Consider removing
world read permissions from files that use %pK, and using dmesg_restrict
to protect against uses of %pK in dmesg(8) if leaking kernel pointer
values to unprivileged users is a concern.
When kptr_restrict is set to (2), kernel pointers printed using
%pK will be replaced with 0's regardless of privileges.
kptr_restrict for hiding kernel pointers from unprivileged users Add the %pK printk format specifier and the /proc/sys/kernel/kptr_restrict sysctl. The %pK format specifier is designed to hide exposed kernel pointers, specifically via /proc interfaces. Exposing these pointers provides an easy target for kernel write vulnerabilities, since they reveal the locations of writable structures containing easily triggerable function pointers. The behavior of %pK depends on the kptr_restrict sysctl. If kptr_restrict is set to 0, no deviation from the standard %p behavior occurs. If kptr_restrict is set to 1, the default, if the current user (intended to be a reader via seq_printf(), etc.) does not have CAP_SYSLOG (currently in the LSM tree), kernel pointers using %pK are printed as 0's. If kptr_restrict is set to 2, kernel pointers using %pK are printed as 0's regardless of privileges. Replacing with 0's was chosen over the default "(null)", which cannot be parsed by userland %p, which expects "(nil)". [akpm@linux-foundation.org: check for IRQ context when !kptr_restrict, save an indent level, s/WARN/WARN_ONCE/] [akpm@linux-foundation.org: coding-style fixup] [randy.dunlap@oracle.com: fix kernel/sysctl.c warning] Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com> Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: James Morris <jmorris@namei.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Thomas Graf <tgraf@infradead.org> Cc: Eugene Teo <eugeneteo@kernel.org> Cc: Kees Cook <kees.cook@canonical.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: David S. Miller <davem@davemloft.net> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Eric Paris <eparis@parisplace.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-01-13 08:59:41 +08:00
==============================================================
kstack_depth_to_print: (X86 only)
Controls the number of words to print when dumping the raw
kernel stack.
==============================================================
l2cr: (PPC only)
This flag controls the L2 cache of G3 processor boards. If
0, the cache is disabled. Enabled if nonzero.
==============================================================
modules_disabled:
A toggle value indicating if modules are allowed to be loaded
in an otherwise modular kernel. This toggle defaults to off
(0), but can be set true (1). Once true, modules can be
neither loaded nor unloaded, and the toggle cannot be set back
kexec: add sysctl to disable kexec_load For general-purpose (i.e. distro) kernel builds it makes sense to build with CONFIG_KEXEC to allow end users to choose what kind of things they want to do with kexec. However, in the face of trying to lock down a system with such a kernel, there needs to be a way to disable kexec_load (much like module loading can be disabled). Without this, it is too easy for the root user to modify kernel memory even when CONFIG_STRICT_DEVMEM and modules_disabled are set. With this change, it is still possible to load an image for use later, then disable kexec_load so the image (or lack of image) can't be altered. The intention is for using this in environments where "perfect" enforcement is hard. Without a verified boot, along with verified modules, and along with verified kexec, this is trying to give a system a better chance to defend itself (or at least grow the window of discoverability) against attack in the face of a privilege escalation. In my mind, I consider several boot scenarios: 1) Verified boot of read-only verified root fs loading fd-based verification of kexec images. 2) Secure boot of writable root fs loading signed kexec images. 3) Regular boot loading kexec (e.g. kcrash) image early and locking it. 4) Regular boot with no control of kexec image at all. 1 and 2 don't exist yet, but will soon once the verified kexec series has landed. 4 is the state of things now. The gap between 2 and 4 is too large, so this change creates scenario 3, a middle-ground above 4 when 2 and 1 are not possible for a system. Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: Rik van Riel <riel@redhat.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Eric Biederman <ebiederm@xmission.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-01-24 07:55:59 +08:00
to false. Generally used with the "kexec_load_disabled" toggle.
==============================================================
msg_next_id, sem_next_id, and shm_next_id:
These three toggles allows to specify desired id for next allocated IPC
object: message, semaphore or shared memory respectively.
By default they are equal to -1, which means generic allocation logic.
Possible values to set are in range {0..INT_MAX}.
Notes:
1) kernel doesn't guarantee, that new object will have desired id. So,
it's up to userspace, how to handle an object with "wrong" id.
2) Toggle with non-default value will be set back to -1 by kernel after
successful IPC object allocation.
==============================================================
nmi_watchdog:
Enables/Disables the NMI watchdog on x86 systems. When the value is
non-zero the NMI watchdog is enabled and will continuously test all
online cpus to determine whether or not they are still functioning
properly. Currently, passing "nmi_watchdog=" parameter at boot time is
required for this function to work.
If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel
parameter), the NMI watchdog shares registers with oprofile. By
disabling the NMI watchdog, oprofile may have more registers to
utilize.
==============================================================
numa_balancing
Enables/disables automatic page fault based NUMA memory
balancing. Memory is moved automatically to nodes
that access it often.
Enables/disables automatic NUMA memory balancing. On NUMA machines, there
is a performance penalty if remote memory is accessed by a CPU. When this
feature is enabled the kernel samples what task thread is accessing memory
by periodically unmapping pages and later trapping a page fault. At the
time of the page fault, it is determined if the data being accessed should
be migrated to a local memory node.
The unmapping of pages and trapping faults incur additional overhead that
ideally is offset by improved memory locality but there is no universal
guarantee. If the target workload is already bound to NUMA nodes then this
feature should be disabled. Otherwise, if the system overhead from the
feature is too high then the rate the kernel samples for NUMA hinting
faults may be controlled by the numa_balancing_scan_period_min_ms,
numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
numa_balancing_scan_size_mb, and numa_balancing_settle_count sysctls.
==============================================================
numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms,
numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb
Automatic NUMA balancing scans tasks address space and unmaps pages to
detect if pages are properly placed or if the data should be migrated to a
memory node local to where the task is running. Every "scan delay" the task
scans the next "scan size" number of pages in its address space. When the
end of the address space is reached the scanner restarts from the beginning.
In combination, the "scan delay" and "scan size" determine the scan rate.
When "scan delay" decreases, the scan rate increases. The scan delay and
hence the scan rate of every task is adaptive and depends on historical
behaviour. If pages are properly placed then the scan delay increases,
otherwise the scan delay decreases. The "scan size" is not adaptive but
the higher the "scan size", the higher the scan rate.
Higher scan rates incur higher system overhead as page faults must be
trapped and potentially data must be migrated. However, the higher the scan
rate, the more quickly a tasks memory is migrated to a local node if the
workload pattern changes and minimises performance impact due to remote
memory accesses. These sysctls control the thresholds for scan delays and
the number of pages scanned.
sched/numa: Set the scan rate proportional to the memory usage of the task being scanned The NUMA PTE scan rate is controlled with a combination of the numa_balancing_scan_period_min, numa_balancing_scan_period_max and numa_balancing_scan_size. This scan rate is independent of the size of the task and as an aside it is further complicated by the fact that numa_balancing_scan_size controls how many pages are marked pte_numa and not how much virtual memory is scanned. In combination, it is almost impossible to meaningfully tune the min and max scan periods and reasoning about performance is complex when the time to complete a full scan is is partially a function of the tasks memory size. This patch alters the semantic of the min and max tunables to be about tuning the length time it takes to complete a scan of a tasks occupied virtual address space. Conceptually this is a lot easier to understand. There is a "sanity" check to ensure the scan rate is never extremely fast based on the amount of virtual memory that should be scanned in a second. The default of 2.5G seems arbitrary but it is to have the maximum scan rate after the patch roughly match the maximum scan rate before the patch was applied. On a similar note, numa_scan_period is in milliseconds and not jiffies. Properly placed pages slow the scanning rate but adding 10 jiffies to numa_scan_period means that the rate scanning slows depends on HZ which is confusing. Get rid of the jiffies_to_msec conversion and treat it as ms. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1381141781-10992-18-git-send-email-mgorman@suse.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-10-07 18:28:55 +08:00
numa_balancing_scan_period_min_ms is the minimum time in milliseconds to
scan a tasks virtual memory. It effectively controls the maximum scanning
rate for each task.
numa_balancing_scan_delay_ms is the starting "scan delay" used for a task
when it initially forks.
sched/numa: Set the scan rate proportional to the memory usage of the task being scanned The NUMA PTE scan rate is controlled with a combination of the numa_balancing_scan_period_min, numa_balancing_scan_period_max and numa_balancing_scan_size. This scan rate is independent of the size of the task and as an aside it is further complicated by the fact that numa_balancing_scan_size controls how many pages are marked pte_numa and not how much virtual memory is scanned. In combination, it is almost impossible to meaningfully tune the min and max scan periods and reasoning about performance is complex when the time to complete a full scan is is partially a function of the tasks memory size. This patch alters the semantic of the min and max tunables to be about tuning the length time it takes to complete a scan of a tasks occupied virtual address space. Conceptually this is a lot easier to understand. There is a "sanity" check to ensure the scan rate is never extremely fast based on the amount of virtual memory that should be scanned in a second. The default of 2.5G seems arbitrary but it is to have the maximum scan rate after the patch roughly match the maximum scan rate before the patch was applied. On a similar note, numa_scan_period is in milliseconds and not jiffies. Properly placed pages slow the scanning rate but adding 10 jiffies to numa_scan_period means that the rate scanning slows depends on HZ which is confusing. Get rid of the jiffies_to_msec conversion and treat it as ms. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1381141781-10992-18-git-send-email-mgorman@suse.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-10-07 18:28:55 +08:00
numa_balancing_scan_period_max_ms is the maximum time in milliseconds to
scan a tasks virtual memory. It effectively controls the minimum scanning
rate for each task.
numa_balancing_scan_size_mb is how many megabytes worth of pages are
scanned for a given scan.
==============================================================
osrelease, ostype & version:
# cat osrelease
2.1.88
# cat ostype
Linux
# cat version
#5 Wed Feb 25 21:49:24 MET 1998
The files osrelease and ostype should be clear enough. Version
needs a little more clarification however. The '#5' means that
this is the fifth kernel built from this source base and the
date behind it indicates the time the kernel was built.
The only way to tune these values is to rebuild the kernel :-)
==============================================================
overflowgid & overflowuid:
if your architecture did not always support 32-bit UIDs (i.e. arm,
i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to
applications that use the old 16-bit UID/GID system calls, if the
actual UID or GID would exceed 65535.
These sysctls allow you to change the value of the fixed UID and GID.
The default is 65534.
==============================================================
panic:
The value in this file represents the number of seconds the kernel
waits before rebooting on a panic. When you use the software watchdog,
the recommended setting is 60.
==============================================================
panic_on_oops:
Controls the kernel's behaviour when an oops or BUG is encountered.
0: try to continue operation
1: panic immediately. If the `panic' sysctl is also non-zero then the
machine will be rebooted.
==============================================================
panic_on_stackoverflow:
Controls the kernel's behavior when detecting the overflows of
kernel, IRQ and exception stacks except a user stack.
This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled.
0: try to continue operation.
1: panic immediately.
==============================================================
kernel: add panic_on_warn There have been several times where I have had to rebuild a kernel to cause a panic when hitting a WARN() in the code in order to get a crash dump from a system. Sometimes this is easy to do, other times (such as in the case of a remote admin) it is not trivial to send new images to the user. A much easier method would be a switch to change the WARN() over to a panic. This makes debugging easier in that I can now test the actual image the WARN() was seen on and I do not have to engage in remote debugging. This patch adds a panic_on_warn kernel parameter and /proc/sys/kernel/panic_on_warn calls panic() in the warn_slowpath_common() path. The function will still print out the location of the warning. An example of the panic_on_warn output: The first line below is from the WARN_ON() to output the WARN_ON()'s location. After that the panic() output is displayed. WARNING: CPU: 30 PID: 11698 at /home/prarit/dummy_module/dummy-module.c:25 init_dummy+0x1f/0x30 [dummy_module]() Kernel panic - not syncing: panic_on_warn set ... CPU: 30 PID: 11698 Comm: insmod Tainted: G W OE 3.17.0+ #57 Hardware name: Intel Corporation S2600CP/S2600CP, BIOS RMLSDP.86I.00.29.D696.1311111329 11/11/2013 0000000000000000 000000008e3f87df ffff88080f093c38 ffffffff81665190 0000000000000000 ffffffff818aea3d ffff88080f093cb8 ffffffff8165e2ec ffffffff00000008 ffff88080f093cc8 ffff88080f093c68 000000008e3f87df Call Trace: [<ffffffff81665190>] dump_stack+0x46/0x58 [<ffffffff8165e2ec>] panic+0xd0/0x204 [<ffffffffa038e05f>] ? init_dummy+0x1f/0x30 [dummy_module] [<ffffffff81076b90>] warn_slowpath_common+0xd0/0xd0 [<ffffffffa038e040>] ? dummy_greetings+0x40/0x40 [dummy_module] [<ffffffff81076c8a>] warn_slowpath_null+0x1a/0x20 [<ffffffffa038e05f>] init_dummy+0x1f/0x30 [dummy_module] [<ffffffff81002144>] do_one_initcall+0xd4/0x210 [<ffffffff811b52c2>] ? __vunmap+0xc2/0x110 [<ffffffff810f8889>] load_module+0x16a9/0x1b30 [<ffffffff810f3d30>] ? store_uevent+0x70/0x70 [<ffffffff810f49b9>] ? copy_module_from_fd.isra.44+0x129/0x180 [<ffffffff810f8ec6>] SyS_finit_module+0xa6/0xd0 [<ffffffff8166cf29>] system_call_fastpath+0x12/0x17 Successfully tested by me. hpa said: There is another very valid use for this: many operators would rather a machine shuts down than being potentially compromised either functionally or security-wise. Signed-off-by: Prarit Bhargava <prarit@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Acked-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> Cc: Fabian Frederick <fabf@skynet.be> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-12-11 07:45:50 +08:00
panic_on_unrecovered_nmi:
The default Linux behaviour on an NMI of either memory or unknown is
to continue operation. For many environments such as scientific
computing it is preferable that the box is taken out and the error
dealt with than an uncorrected parity/ECC error get propagated.
A small number of systems do generate NMI's for bizarre random reasons
such as power management so the default is off. That sysctl works like
the existing panic controls already in that directory.
==============================================================
panic_on_warn:
Calls panic() in the WARN() path when set to 1. This is useful to avoid
a kernel rebuild when attempting to kdump at the location of a WARN().
0: only WARN(), default behaviour.
1: call panic() after printing out WARN() location.
==============================================================
perf_cpu_time_max_percent:
Hints to the kernel how much CPU time it should be allowed to
use to handle perf sampling events. If the perf subsystem
is informed that its samples are exceeding this limit, it
will drop its sampling frequency to attempt to reduce its CPU
usage.
Some perf sampling happens in NMIs. If these samples
unexpectedly take too long to execute, the NMIs can become
stacked up next to each other so much that nothing else is
allowed to execute.
0: disable the mechanism. Do not monitor or correct perf's
sampling rate no matter how CPU time it takes.
1-100: attempt to throttle perf's sample rate to this
percentage of CPU. Note: the kernel calculates an
"expected" length of each sample event. 100 here means
100% of that expected length. Even if this is set to
100, you may still see sample throttling if this
length is exceeded. Set to 0 if you truly do not care
how much CPU is consumed.
==============================================================
pid_max:
PID allocation wrap value. When the kernel's next PID value
reaches this value, it wraps back to a minimum PID value.
PIDs of value pid_max or larger are not allocated.
==============================================================
ns_last_pid:
The last pid allocated in the current (the one task using this sysctl
lives in) pid namespace. When selecting a pid for a next task on fork
kernel tries to allocate a number starting from this one.
==============================================================
powersave-nap: (PPC only)
If set, Linux-PPC will use the 'nap' mode of powersaving,
otherwise the 'doze' mode will be used.
==============================================================
printk:
The four values in printk denote: console_loglevel,
default_message_loglevel, minimum_console_loglevel and
default_console_loglevel respectively.
These values influence printk() behavior when printing or
logging error messages. See 'man 2 syslog' for more info on
the different loglevels.
- console_loglevel: messages with a higher priority than
this will be printed to the console
- default_message_loglevel: messages without an explicit priority
will be printed with this priority
- minimum_console_loglevel: minimum (highest) value to which
console_loglevel can be set
- default_console_loglevel: default value for console_loglevel
==============================================================
printk_delay:
Delay each printk message in printk_delay milliseconds
Value from 0 - 10000 is allowed.
==============================================================
printk_ratelimit:
Some warning messages are rate limited. printk_ratelimit specifies
the minimum length of time between these messages (in jiffies), by
default we allow one every 5 seconds.
A value of 0 will disable rate limiting.
==============================================================
printk_ratelimit_burst:
While long term we enforce one message per printk_ratelimit
seconds, we do allow a burst of messages to pass through.
printk_ratelimit_burst specifies the number of messages we can
send before ratelimiting kicks in.
==============================================================
randomize_va_space:
This option can be used to select the type of process address
space randomization that is used in the system, for architectures
that support this feature.
0 - Turn the process address space randomization off. This is the
default for architectures that do not support this feature anyways,
and kernels that are booted with the "norandmaps" parameter.
1 - Make the addresses of mmap base, stack and VDSO page randomized.
This, among other things, implies that shared libraries will be
loaded to random addresses. Also for PIE-linked binaries, the
location of code start is randomized. This is the default if the
CONFIG_COMPAT_BRK option is enabled.
2 - Additionally enable heap randomization. This is the default if
CONFIG_COMPAT_BRK is disabled.
There are a few legacy applications out there (such as some ancient
versions of libc.so.5 from 1996) that assume that brk area starts
just after the end of the code+bss. These applications break when
start of the brk area is randomized. There are however no known
non-legacy applications that would be broken this way, so for most
systems it is safe to choose full randomization.
Systems with ancient and/or broken binaries should be configured
with CONFIG_COMPAT_BRK enabled, which excludes the heap from process
address space randomization.
==============================================================
reboot-cmd: (Sparc only)
??? This seems to be a way to give an argument to the Sparc
ROM/Flash boot loader. Maybe to tell it what to do after
rebooting. ???
==============================================================
rtsig-max & rtsig-nr:
The file rtsig-max can be used to tune the maximum number
of POSIX realtime (queued) signals that can be outstanding
in the system.
rtsig-nr shows the number of RT signals currently queued.
==============================================================
sg-big-buff:
This file shows the size of the generic SCSI (sg) buffer.
You can't tune it just yet, but you could change it on
compile time by editing include/scsi/sg.h and changing
the value of SG_BIG_BUFF.
There shouldn't be any reason to change this value. If
you can come up with one, you probably know what you
are doing anyway :)
==============================================================
shmall:
This parameter sets the total amount of shared memory pages that
can be used system wide. Hence, SHMALL should always be at least
ceil(shmmax/PAGE_SIZE).
If you are not sure what the default PAGE_SIZE is on your Linux
system, you can run the following command:
# getconf PAGE_SIZE
==============================================================
shmmax:
This value can be used to query and set the run time limit
on the maximum shared memory segment size that can be created.
Shared memory segments up to 1Gb are now supported in the
kernel. This value defaults to SHMMAX.
==============================================================
ipc: introduce shm_rmid_forced sysctl Add support for the shm_rmid_forced sysctl. If set to 1, all shared memory objects in current ipc namespace will be automatically forced to use IPC_RMID. The POSIX way of handling shmem allows one to create shm objects and call shmdt(), leaving shm object associated with no process, thus consuming memory not counted via rlimits. With shm_rmid_forced=1 the shared memory object is counted at least for one process, so OOM killer may effectively kill the fat process holding the shared memory. It obviously breaks POSIX - some programs relying on the feature would stop working. So set shm_rmid_forced=1 only if you're sure nobody uses "orphaned" memory. Use shm_rmid_forced=0 by default for compatability reasons. The feature was previously impemented in -ow as a configure option. [akpm@linux-foundation.org: fix documentation, per Randy] [akpm@linux-foundation.org: fix warning] [akpm@linux-foundation.org: readability/conventionality tweaks] [akpm@linux-foundation.org: fix shm_rmid_forced/shm_forced_rmid confusion, use standard comment layout] Signed-off-by: Vasiliy Kulikov <segoon@openwall.com> Cc: Randy Dunlap <rdunlap@xenotime.net> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: "Serge E. Hallyn" <serge.hallyn@canonical.com> Cc: Daniel Lezcano <daniel.lezcano@free.fr> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Tejun Heo <tj@kernel.org> Cc: Ingo Molnar <mingo@elte.hu> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Solar Designer <solar@openwall.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-07-27 07:08:48 +08:00
shm_rmid_forced:
Linux lets you set resource limits, including how much memory one
process can consume, via setrlimit(2). Unfortunately, shared memory
segments are allowed to exist without association with any process, and
thus might not be counted against any resource limits. If enabled,
shared memory segments are automatically destroyed when their attach
count becomes zero after a detach or a process termination. It will
also destroy segments that were created, but never attached to, on exit
from the process. The only use left for IPC_RMID is to immediately
destroy an unattached segment. Of course, this breaks the way things are
defined, so some applications might stop working. Note that this
feature will do you no good unless you also configure your resource
limits (in particular, RLIMIT_AS and RLIMIT_NPROC). Most systems don't
need this.
Note that if you change this from 0 to 1, already created segments
without users and with a dead originative process will be destroyed.
==============================================================
sysctl: allow for strict write position handling When writing to a sysctl string, each write, regardless of VFS position, begins writing the string from the start. This means the contents of the last write to the sysctl controls the string contents instead of the first: open("/proc/sys/kernel/modprobe", O_WRONLY) = 1 write(1, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 4096) = 4096 write(1, "/bin/true", 9) = 9 close(1) = 0 $ cat /proc/sys/kernel/modprobe /bin/true Expected behaviour would be to have the sysctl be "AAAA..." capped at maxlen (in this case KMOD_PATH_LEN: 256), instead of truncating to the contents of the second write. Similarly, multiple short writes would not append to the sysctl. The old behavior is unlike regular POSIX files enough that doing audits of software that interact with sysctls can end up in unexpected or dangerous situations. For example, "as long as the input starts with a trusted path" turns out to be an insufficient filter, as what must also happen is for the input to be entirely contained in a single write syscall -- not a common consideration, especially for high level tools. This provides kernel.sysctl_writes_strict as a way to make this behavior act in a less surprising manner for strings, and disallows non-zero file position when writing numeric sysctls (similar to what is already done when reading from non-zero file positions). For now, the default (0) is to warn about non-zero file position use, but retain the legacy behavior. Setting this to -1 disables the warning, and setting this to 1 enables the file position respecting behavior. [akpm@linux-foundation.org: fix build] [akpm@linux-foundation.org: move misplaced hunk, per Randy] Signed-off-by: Kees Cook <keescook@chromium.org> Cc: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-07 05:37:19 +08:00
sysctl_writes_strict:
Control how file position affects the behavior of updating sysctl values
via the /proc/sys interface:
-1 - Legacy per-write sysctl value handling, with no printk warnings.
Each write syscall must fully contain the sysctl value to be
written, and multiple writes on the same sysctl file descriptor
will rewrite the sysctl value, regardless of file position.
0 - (default) Same behavior as above, but warn about processes that
perform writes to a sysctl file descriptor when the file position
is not 0.
1 - Respect file position when writing sysctl strings. Multiple writes
will append to the sysctl value buffer. Anything past the max length
of the sysctl value buffer will be ignored. Writes to numeric sysctl
entries must always be at file position 0 and the value must be
fully contained in the buffer sent in the write syscall.
==============================================================
kernel/watchdog.c: print traces for all cpus on lockup detection A 'softlockup' is defined as a bug that causes the kernel to loop in kernel mode for more than a predefined period to time, without giving other tasks a chance to run. Currently, upon detection of this condition by the per-cpu watchdog task, debug information (including a stack trace) is sent to the system log. On some occasions, we have observed that the "victim" rather than the actual "culprit" (i.e. the owner/holder of the contended resource) is reported to the user. Often this information has proven to be insufficient to assist debugging efforts. To avoid loss of useful debug information, for architectures which support NMI, this patch makes it possible to improve soft lockup reporting. This is accomplished by issuing an NMI to each cpu to obtain a stack trace. If NMI is not supported we just revert back to the old method. A sysctl and boot-time parameter is available to toggle this feature. [dzickus@redhat.com: add CONFIG_SMP in certain areas] [akpm@linux-foundation.org: additional CONFIG_SMP=n optimisations] [mq@suse.cz: fix warning] Signed-off-by: Aaron Tomlin <atomlin@redhat.com> Signed-off-by: Don Zickus <dzickus@redhat.com> Cc: David S. Miller <davem@davemloft.net> Cc: Mateusz Guzik <mguzik@redhat.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Jan Moskyto Matejka <mq@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-24 04:22:05 +08:00
softlockup_all_cpu_backtrace:
This value controls the soft lockup detector thread's behavior
when a soft lockup condition is detected as to whether or not
to gather further debug information. If enabled, each cpu will
be issued an NMI and instructed to capture stack trace.
This feature is only applicable for architectures which support
NMI.
0: do nothing. This is the default behavior.
1: on detection capture more debug information.
==============================================================
tainted:
Non-zero if the kernel has been tainted. Numeric values, which
can be ORed together:
1 - A module with a non-GPL license has been loaded, this
includes modules with no license.
Set by modutils >= 2.4.9 and module-init-tools.
2 - A module was force loaded by insmod -f.
Set by modutils >= 2.4.9 and module-init-tools.
4 - Unsafe SMP processors: SMP with CPUs not designed for SMP.
8 - A module was forcibly unloaded from the system by rmmod -f.
16 - A hardware machine check error occurred on the system.
32 - A bad page was discovered on the system.
64 - The user has asked that the system be marked "tainted". This
could be because they are running software that directly modifies
the hardware, or for other reasons.
128 - The system has died.
256 - The ACPI DSDT has been overridden with one supplied by the user
instead of using the one provided by the hardware.
512 - A kernel warning has occurred.
1024 - A module from drivers/staging was loaded.
2048 - The system is working around a severe firmware bug.
4096 - An out-of-tree module has been loaded.
Fix: module signature vs tracepoints: add new TAINT_UNSIGNED_MODULE Users have reported being unable to trace non-signed modules loaded within a kernel supporting module signature. This is caused by tracepoint.c:tracepoint_module_coming() refusing to take into account tracepoints sitting within force-loaded modules (TAINT_FORCED_MODULE). The reason for this check, in the first place, is that a force-loaded module may have a struct module incompatible with the layout expected by the kernel, and can thus cause a kernel crash upon forced load of that module on a kernel with CONFIG_TRACEPOINTS=y. Tracepoints, however, specifically accept TAINT_OOT_MODULE and TAINT_CRAP, since those modules do not lead to the "very likely system crash" issue cited above for force-loaded modules. With kernels having CONFIG_MODULE_SIG=y (signed modules), a non-signed module is tainted re-using the TAINT_FORCED_MODULE taint flag. Unfortunately, this means that Tracepoints treat that module as a force-loaded module, and thus silently refuse to consider any tracepoint within this module. Since an unsigned module does not fit within the "very likely system crash" category of tainting, add a new TAINT_UNSIGNED_MODULE taint flag to specifically address this taint behavior, and accept those modules within Tracepoints. We use the letter 'X' as a taint flag character for a module being loaded that doesn't know how to sign its name (proposed by Steven Rostedt). Also add the missing 'O' entry to trace event show_module_flags() list for the sake of completeness. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Acked-by: Steven Rostedt <rostedt@goodmis.org> NAKed-by: Ingo Molnar <mingo@redhat.com> CC: Thomas Gleixner <tglx@linutronix.de> CC: David Howells <dhowells@redhat.com> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2014-03-13 09:41:30 +08:00
8192 - An unsigned module has been loaded in a kernel supporting module
signature.
16384 - A soft lockup has previously occurred on the system.
32768 - The kernel has been live patched.
documentation: update Documentation/filesystem/proc.txt and Documentation/sysctls Now /proc/sys is described in many places and much information is redundant. This patch updates the proc.txt and move the /proc/sys desciption out to the files in Documentation/sysctls. Details are: merge - 2.1 /proc/sys/fs - File system data - 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem - 2.17 /proc/sys/fs/epoll - Configuration options for the epoll interface with Documentation/sysctls/fs.txt. remove - 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats since it's not better then the Documentation/binfmt_misc.txt. merge - 2.3 /proc/sys/kernel - general kernel parameters with Documentation/sysctls/kernel.txt remove - 2.5 /proc/sys/dev - Device specific parameters since it's obsolete the sysfs is used now. remove - 2.6 /proc/sys/sunrpc - Remote procedure calls since it's not better then the Documentation/sysctls/sunrpc.txt move - 2.7 /proc/sys/net - Networking stuff - 2.9 Appletalk - 2.10 IPX to newly created Documentation/sysctls/net.txt. remove - 2.8 /proc/sys/net/ipv4 - IPV4 settings since it's not better then the Documentation/networking/ip-sysctl.txt. add - Chapter 3 Per-Process Parameters to descibe /proc/<pid>/xxx parameters. Signed-off-by: Shen Feng <shen@cn.fujitsu.com> Cc: Randy Dunlap <randy.dunlap@oracle.com> Cc: "David S. Miller" <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-03 07:57:20 +08:00
==============================================================
unknown_nmi_panic:
The value in this file affects behavior of handling NMI. When the
value is non-zero, unknown NMI is trapped and then panic occurs. At
that time, kernel debugging information is displayed on console.
documentation: update Documentation/filesystem/proc.txt and Documentation/sysctls Now /proc/sys is described in many places and much information is redundant. This patch updates the proc.txt and move the /proc/sys desciption out to the files in Documentation/sysctls. Details are: merge - 2.1 /proc/sys/fs - File system data - 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem - 2.17 /proc/sys/fs/epoll - Configuration options for the epoll interface with Documentation/sysctls/fs.txt. remove - 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats since it's not better then the Documentation/binfmt_misc.txt. merge - 2.3 /proc/sys/kernel - general kernel parameters with Documentation/sysctls/kernel.txt remove - 2.5 /proc/sys/dev - Device specific parameters since it's obsolete the sysfs is used now. remove - 2.6 /proc/sys/sunrpc - Remote procedure calls since it's not better then the Documentation/sysctls/sunrpc.txt move - 2.7 /proc/sys/net - Networking stuff - 2.9 Appletalk - 2.10 IPX to newly created Documentation/sysctls/net.txt. remove - 2.8 /proc/sys/net/ipv4 - IPV4 settings since it's not better then the Documentation/networking/ip-sysctl.txt. add - Chapter 3 Per-Process Parameters to descibe /proc/<pid>/xxx parameters. Signed-off-by: Shen Feng <shen@cn.fujitsu.com> Cc: Randy Dunlap <randy.dunlap@oracle.com> Cc: "David S. Miller" <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-03 07:57:20 +08:00
NMI switch that most IA32 servers have fires unknown NMI up, for
example. If a system hangs up, try pressing the NMI switch.
==============================================================
watchdog_thresh:
This value can be used to control the frequency of hrtimer and NMI
events and the soft and hard lockup thresholds. The default threshold
is 10 seconds.
The softlockup threshold is (2 * watchdog_thresh). Setting this
tunable to zero will disable lockup detection altogether.
==============================================================