aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/sysctl/kernel.txt
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/sysctl/kernel.txt')
-rw-r--r--Documentation/sysctl/kernel.txt237
1 files changed, 132 insertions, 105 deletions
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 5e7cb39ad19..704e474a93d 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -17,23 +17,21 @@ before actually making adjustments.
17 17
18Currently, these files might (depending on your configuration) 18Currently, these files might (depending on your configuration)
19show up in /proc/sys/kernel: 19show up in /proc/sys/kernel:
20- acpi_video_flags 20
21- acct 21- acct
22- acpi_video_flags
23- auto_msgmni
22- bootloader_type [ X86 only ] 24- bootloader_type [ X86 only ]
23- bootloader_version [ X86 only ] 25- bootloader_version [ X86 only ]
24- callhome [ S390 only ] 26- callhome [ S390 only ]
25- auto_msgmni
26- core_pattern 27- core_pattern
27- core_pipe_limit 28- core_pipe_limit
28- core_uses_pid 29- core_uses_pid
29- ctrl-alt-del 30- ctrl-alt-del
30- dentry-state
31- dmesg_restrict 31- dmesg_restrict
32- domainname 32- domainname
33- hostname 33- hostname
34- hotplug 34- hotplug
35- java-appletviewer [ binfmt_java, obsolete ]
36- java-interpreter [ binfmt_java, obsolete ]
37- kptr_restrict 35- kptr_restrict
38- kstack_depth_to_print [ X86 only ] 36- kstack_depth_to_print [ X86 only ]
39- l2cr [ PPC only ] 37- l2cr [ PPC only ]
@@ -48,10 +46,14 @@ show up in /proc/sys/kernel:
48- overflowgid 46- overflowgid
49- overflowuid 47- overflowuid
50- panic 48- panic
49- panic_on_oops
50- panic_on_unrecovered_nmi
51- pid_max 51- pid_max
52- powersave-nap [ PPC only ] 52- powersave-nap [ PPC only ]
53- panic_on_unrecovered_nmi
54- printk 53- printk
54- printk_delay
55- printk_ratelimit
56- printk_ratelimit_burst
55- randomize_va_space 57- randomize_va_space
56- real-root-dev ==> Documentation/initrd.txt 58- real-root-dev ==> Documentation/initrd.txt
57- reboot-cmd [ SPARC only ] 59- reboot-cmd [ SPARC only ]
@@ -59,9 +61,11 @@ show up in /proc/sys/kernel:
59- rtsig-nr 61- rtsig-nr
60- sem 62- sem
61- sg-big-buff [ generic SCSI device (sg) ] 63- sg-big-buff [ generic SCSI device (sg) ]
64- shm_rmid_forced
62- shmall 65- shmall
63- shmmax [ sysv ipc ] 66- shmmax [ sysv ipc ]
64- shmmni 67- shmmni
68- softlockup_thresh
65- stop-a [ SPARC only ] 69- stop-a [ SPARC only ]
66- sysrq ==> Documentation/sysrq.txt 70- sysrq ==> Documentation/sysrq.txt
67- tainted 71- tainted
@@ -71,15 +75,6 @@ show up in /proc/sys/kernel:
71 75
72============================================================== 76==============================================================
73 77
74acpi_video_flags:
75
76flags
77
78See Doc*/kernel/power/video.txt, it allows mode of video boot to be
79set during run time.
80
81==============================================================
82
83acct: 78acct:
84 79
85highwater lowwater frequency 80highwater lowwater frequency
@@ -97,6 +92,25 @@ valid for 30 seconds.
97 92
98============================================================== 93==============================================================
99 94
95acpi_video_flags:
96
97flags
98
99See Doc*/kernel/power/video.txt, it allows mode of video boot to be
100set during run time.
101
102==============================================================
103
104auto_msgmni:
105
106Enables/Disables automatic recomputing of msgmni upon memory add/remove
107or upon ipc namespace creation/removal (see the msgmni description
108above). Echoing "1" into this file enables msgmni automatic recomputing.
109Echoing "0" turns it off. auto_msgmni default value is 1.
110
111
112==============================================================
113
100bootloader_type: 114bootloader_type:
101 115
102x86 bootloader identification 116x86 bootloader identification
@@ -172,22 +186,24 @@ core_pattern is used to specify a core dumpfile pattern name.
172 186
173core_pipe_limit: 187core_pipe_limit:
174 188
175This sysctl is only applicable when core_pattern is configured to pipe core 189This sysctl is only applicable when core_pattern is configured to pipe
176files to a user space helper (when the first character of core_pattern is a '|', 190core files to a user space helper (when the first character of
177see above). When collecting cores via a pipe to an application, it is 191core_pattern is a '|', see above). When collecting cores via a pipe
178occasionally useful for the collecting application to gather data about the 192to an application, it is occasionally useful for the collecting
179crashing process from its /proc/pid directory. In order to do this safely, the 193application to gather data about the crashing process from its
180kernel must wait for the collecting process to exit, so as not to remove the 194/proc/pid directory. In order to do this safely, the kernel must wait
181crashing processes proc files prematurely. This in turn creates the possibility 195for the collecting process to exit, so as not to remove the crashing
182that a misbehaving userspace collecting process can block the reaping of a 196processes proc files prematurely. This in turn creates the
183crashed process simply by never exiting. This sysctl defends against that. It 197possibility that a misbehaving userspace collecting process can block
184defines how many concurrent crashing processes may be piped to user space 198the reaping of a crashed process simply by never exiting. This sysctl
185applications in parallel. If this value is exceeded, then those crashing 199defends against that. It defines how many concurrent crashing
186processes above that value are noted via the kernel log and their cores are 200processes may be piped to user space applications in parallel. If
187skipped. 0 is a special value, indicating that unlimited processes may be 201this value is exceeded, then those crashing processes above that value
188captured in parallel, but that no waiting will take place (i.e. the collecting 202are noted via the kernel log and their cores are skipped. 0 is a
189process is not guaranteed access to /proc/<crashing pid>/). This value defaults 203special value, indicating that unlimited processes may be captured in
190to 0. 204parallel, but that no waiting will take place (i.e. the collecting
205process is not guaranteed access to /proc/<crashing pid>/). This
206value defaults to 0.
191 207
192============================================================== 208==============================================================
193 209
@@ -218,14 +234,14 @@ to decide what to do with it.
218 234
219dmesg_restrict: 235dmesg_restrict:
220 236
221This toggle indicates whether unprivileged users are prevented from using 237This toggle indicates whether unprivileged users are prevented
222dmesg(8) to view messages from the kernel's log buffer. When 238from using dmesg(8) to view messages from the kernel's log buffer.
223dmesg_restrict is set to (0) there are no restrictions. When 239When dmesg_restrict is set to (0) there are no restrictions. When
224dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use 240dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use
225dmesg(8). 241dmesg(8).
226 242
227The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the default 243The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the
228value of dmesg_restrict. 244default value of dmesg_restrict.
229 245
230============================================================== 246==============================================================
231 247
@@ -256,13 +272,6 @@ Default value is "/sbin/hotplug".
256 272
257============================================================== 273==============================================================
258 274
259l2cr: (PPC only)
260
261This flag controls the L2 cache of G3 processor boards. If
2620, the cache is disabled. Enabled if nonzero.
263
264==============================================================
265
266kptr_restrict: 275kptr_restrict:
267 276
268This toggle indicates whether restrictions are placed on 277This toggle indicates whether restrictions are placed on
@@ -283,6 +292,13 @@ kernel stack.
283 292
284============================================================== 293==============================================================
285 294
295l2cr: (PPC only)
296
297This flag controls the L2 cache of G3 processor boards. If
2980, the cache is disabled. Enabled if nonzero.
299
300==============================================================
301
286modules_disabled: 302modules_disabled:
287 303
288A toggle value indicating if modules are allowed to be loaded 304A toggle value indicating if modules are allowed to be loaded
@@ -293,6 +309,21 @@ to false.
293 309
294============================================================== 310==============================================================
295 311
312nmi_watchdog:
313
314Enables/Disables the NMI watchdog on x86 systems. When the value is
315non-zero the NMI watchdog is enabled and will continuously test all
316online cpus to determine whether or not they are still functioning
317properly. Currently, passing "nmi_watchdog=" parameter at boot time is
318required for this function to work.
319
320If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel
321parameter), the NMI watchdog shares registers with oprofile. By
322disabling the NMI watchdog, oprofile may have more registers to
323utilize.
324
325==============================================================
326
296osrelease, ostype & version: 327osrelease, ostype & version:
297 328
298# cat osrelease 329# cat osrelease
@@ -312,10 +343,10 @@ The only way to tune these values is to rebuild the kernel :-)
312 343
313overflowgid & overflowuid: 344overflowgid & overflowuid:
314 345
315if your architecture did not always support 32-bit UIDs (i.e. arm, i386, 346if your architecture did not always support 32-bit UIDs (i.e. arm,
316m68k, sh, and sparc32), a fixed UID and GID will be returned to 347i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to
317applications that use the old 16-bit UID/GID system calls, if the actual 348applications that use the old 16-bit UID/GID system calls, if the
318UID or GID would exceed 65535. 349actual UID or GID would exceed 65535.
319 350
320These sysctls allow you to change the value of the fixed UID and GID. 351These sysctls allow you to change the value of the fixed UID and GID.
321The default is 65534. 352The default is 65534.
@@ -324,9 +355,22 @@ The default is 65534.
324 355
325panic: 356panic:
326 357
327The value in this file represents the number of seconds the 358The value in this file represents the number of seconds the kernel
328kernel waits before rebooting on a panic. When you use the 359waits before rebooting on a panic. When you use the software watchdog,
329software watchdog, the recommended setting is 60. 360the recommended setting is 60.
361
362==============================================================
363
364panic_on_unrecovered_nmi:
365
366The default Linux behaviour on an NMI of either memory or unknown is
367to continue operation. For many environments such as scientific
368computing it is preferable that the box is taken out and the error
369dealt with than an uncorrected parity/ECC error get propagated.
370
371A small number of systems do generate NMI's for bizarre random reasons
372such as power management so the default is off. That sysctl works like
373the existing panic controls already in that directory.
330 374
331============================================================== 375==============================================================
332 376
@@ -376,6 +420,14 @@ the different loglevels.
376 420
377============================================================== 421==============================================================
378 422
423printk_delay:
424
425Delay each printk message in printk_delay milliseconds
426
427Value from 0 - 10000 is allowed.
428
429==============================================================
430
379printk_ratelimit: 431printk_ratelimit:
380 432
381Some warning messages are rate limited. printk_ratelimit specifies 433Some warning messages are rate limited. printk_ratelimit specifies
@@ -395,15 +447,7 @@ send before ratelimiting kicks in.
395 447
396============================================================== 448==============================================================
397 449
398printk_delay: 450randomize_va_space:
399
400Delay each printk message in printk_delay milliseconds
401
402Value from 0 - 10000 is allowed.
403
404==============================================================
405
406randomize-va-space:
407 451
408This option can be used to select the type of process address 452This option can be used to select the type of process address
409space randomization that is used in the system, for architectures 453space randomization that is used in the system, for architectures
@@ -466,15 +510,36 @@ are doing anyway :)
466 510
467============================================================== 511==============================================================
468 512
469shmmax: 513shmmax:
470 514
471This value can be used to query and set the run time limit 515This value can be used to query and set the run time limit
472on the maximum shared memory segment size that can be created. 516on the maximum shared memory segment size that can be created.
473Shared memory segments up to 1Gb are now supported in the 517Shared memory segments up to 1Gb are now supported in the
474kernel. This value defaults to SHMMAX. 518kernel. This value defaults to SHMMAX.
475 519
476============================================================== 520==============================================================
477 521
522shm_rmid_forced:
523
524Linux lets you set resource limits, including how much memory one
525process can consume, via setrlimit(2). Unfortunately, shared memory
526segments are allowed to exist without association with any process, and
527thus might not be counted against any resource limits. If enabled,
528shared memory segments are automatically destroyed when their attach
529count becomes zero after a detach or a process termination. It will
530also destroy segments that were created, but never attached to, on exit
531from the process. The only use left for IPC_RMID is to immediately
532destroy an unattached segment. Of course, this breaks the way things are
533defined, so some applications might stop working. Note that this
534feature will do you no good unless you also configure your resource
535limits (in particular, RLIMIT_AS and RLIMIT_NPROC). Most systems don't
536need this.
537
538Note that if you change this from 0 to 1, already created segments
539without users and with a dead originative process will be destroyed.
540
541==============================================================
542
478softlockup_thresh: 543softlockup_thresh:
479 544
480This value can be used to lower the softlockup tolerance threshold. The 545This value can be used to lower the softlockup tolerance threshold. The
@@ -484,7 +549,7 @@ tunable to zero will disable the softlockup detection altogether.
484 549
485============================================================== 550==============================================================
486 551
487tainted: 552tainted:
488 553
489Non-zero if the kernel has been tainted. Numeric values, which 554Non-zero if the kernel has been tainted. Numeric values, which
490can be ORed together: 555can be ORed together:
@@ -509,49 +574,11 @@ can be ORed together:
509 574
510============================================================== 575==============================================================
511 576
512auto_msgmni:
513
514Enables/Disables automatic recomputing of msgmni upon memory add/remove or
515upon ipc namespace creation/removal (see the msgmni description above).
516Echoing "1" into this file enables msgmni automatic recomputing.
517Echoing "0" turns it off.
518auto_msgmni default value is 1.
519
520==============================================================
521
522nmi_watchdog:
523
524Enables/Disables the NMI watchdog on x86 systems. When the value is non-zero
525the NMI watchdog is enabled and will continuously test all online cpus to
526determine whether or not they are still functioning properly. Currently,
527passing "nmi_watchdog=" parameter at boot time is required for this function
528to work.
529
530If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel parameter), the
531NMI watchdog shares registers with oprofile. By disabling the NMI watchdog,
532oprofile may have more registers to utilize.
533
534==============================================================
535
536unknown_nmi_panic: 577unknown_nmi_panic:
537 578
538The value in this file affects behavior of handling NMI. When the value is 579The value in this file affects behavior of handling NMI. When the
539non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel 580value is non-zero, unknown NMI is trapped and then panic occurs. At
540debugging information is displayed on console. 581that time, kernel debugging information is displayed on console.
541
542NMI switch that most IA32 servers have fires unknown NMI up, for example.
543If a system hangs up, try pressing the NMI switch.
544
545==============================================================
546
547panic_on_unrecovered_nmi:
548
549The default Linux behaviour on an NMI of either memory or unknown is to continue
550operation. For many environments such as scientific computing it is preferable
551that the box is taken out and the error dealt with than an uncorrected
552parity/ECC error get propogated.
553
554A small number of systems do generate NMI's for bizarre random reasons such as
555power management so the default is off. That sysctl works like the existing
556panic controls already in that directory.
557 582
583NMI switch that most IA32 servers have fires unknown NMI up, for
584example. If a system hangs up, try pressing the NMI switch.