1 Documentation for /proc/sys/kernel/* kernel version 2.2.10
2 (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
4 For general info and legal blurb, please look in README.
6 ==============================================================
8 This file contains documentation for the sysctl files in
9 /proc/sys/kernel/ and is valid for Linux kernel version 2.2.
11 The files in this directory can be used to tune and monitor
12 miscellaneous and general things in the operation of the Linux
13 kernel. Since some of the files _can_ be used to screw up your
14 system, it is advisable to read both documentation and source
15 before actually making adjustments.
17 Currently, these files might (depending on your configuration)
18 show up in /proc/sys/kernel:
24 - htab-reclaim [ PPC only ]
25 - java-appletviewer [ binfmt_java, obsolete ]
26 - java-interpreter [ binfmt_java, obsolete ]
28 - modprobe ==> Documentation/kmod.txt
34 - powersave-nap [ PPC only ]
36 - real-root-dev ==> Documentation/initrd.txt
37 - reboot-cmd [ SPARC only ]
40 - sg-big-buff [ generic SCSI device (sg) ]
44 - zero-paged [ PPC only ]
46 ==============================================================
50 highwater lowwater frequency
52 If BSD-style process accounting is enabled these values control
53 its behaviour. If free space on filesystem where the log lives
54 goes below <lowwater>% accounting suspends. If free space gets
55 above <highwater>% accounting resumes. <Frequency> determines
56 how often do we check the amount of free space (value is in
59 That is, suspend accounting if there left <= 2% free; resume it
60 if we got >=4%; consider information about amount of free space
63 ==============================================================
67 When the value in this file is 0, ctrl-alt-del is trapped and
68 sent to the init(1) program to handle a graceful restart.
69 When, however, the value is > 0, Linux's reaction to a Vulcan
70 Nerve Pinch (tm) will be an immediate reboot, without even
71 syncing its dirty buffers.
73 Note: when a program (like dosemu) has the keyboard in 'raw'
74 mode, the ctrl-alt-del is intercepted by the program before it
75 ever reaches the kernel tty layer, and it's up to the program
76 to decide what to do with it.
78 ==============================================================
80 domainname & hostname:
82 These files can be used to set the NIS/YP domainname and the
83 hostname of your box in exactly the same way as the commands
84 domainname and hostname, i.e.:
85 # echo "darkstar" > /proc/sys/kernel/hostname
86 # echo "mydomain" > /proc/sys/kernel/domainname
87 has the same effect as
88 # hostname "darkstar" > /proc/sys/kernel/hostname
89 # domainname "mydomain" > /proc/sys/kernel/domainname
91 Note, however, that the classic darkstar.frop.org has the
92 hostname "darkstar" and DNS (Internet Domain Name Server)
93 domainname "frop.org", not to be confused with the NIS (Network
94 Information Service) or YP (Yellow Pages) domainname. These two
95 domain names are in general different. For a detailed discussion
96 see the hostname(1) man page.
98 ==============================================================
100 htab-reclaim: (PPC only)
102 Setting this to a non-zero value, the PowerPC htab
103 (see Documentation/powerpc/ppc_htab.txt) is pruned
104 each time the system hits the idle loop.
106 ==============================================================
110 This flag controls the L2 cache of G3 processor boards. If
111 0, the cache is disabled. Enabled if nonzero.
113 ==============================================================
115 osrelease, ostype & version:
122 #5 Wed Feb 25 21:49:24 MET 1998
124 The files osrelease and ostype should be clear enough. Version
125 needs a little more clarification however. The '#5' means that
126 this is the fifth kernel built from this source base and the
127 date behind it indicates the time the kernel was built.
128 The only way to tune these values is to rebuild the kernel :-)
130 ==============================================================
132 overflowgid & overflowuid:
134 if your architecture did not always support 32-bit UIDs (i.e. arm, i386,
135 m68k, sh, and sparc32), a fixed UID and GID will be returned to
136 applications that use the old 16-bit UID/GID system calls, if the actual
137 UID or GID would exceed 65535.
139 These sysctls allow you to change the value of the fixed UID and GID.
140 The default is 65534.
142 ==============================================================
146 The value in this file represents the number of seconds the
147 kernel waits before rebooting on a panic. When you use the
148 software watchdog, the recommended setting is 60.
150 ==============================================================
152 powersave-nap: (PPC only)
154 If set, Linux-PPC will use the 'nap' mode of powersaving,
155 otherwise the 'doze' mode will be used.
157 ==============================================================
161 The four values in printk denote: console_loglevel,
162 default_message_loglevel, minimum_console_level and
163 default_console_loglevel respectively.
165 These values influence printk() behavior when printing or
166 logging error messages. See 'man 2 syslog' for more info on
167 the different loglevels.
169 - console_loglevel: messages with a higher priority than
170 this will be printed to the console
171 - default_message_level: messages without an explicit priority
172 will be printed with this priority
173 - minimum_console_loglevel: minimum (highest) value to which
174 console_loglevel can be set
175 - default_console_loglevel: default value for console_loglevel
177 Note: a quick look in linux/kernel/printk.c will reveal that
178 these variables aren't put inside a structure, so their order
179 in-core isn't formally guaranteed and garbage values _might_
180 occur when the compiler changes. (???)
182 ==============================================================
184 reboot-cmd: (Sparc only)
186 ??? This seems to be a way to give an argument to the Sparc
187 ROM/Flash boot loader. Maybe to tell it what to do after
190 ==============================================================
192 rtsig-max & rtsig-nr:
194 The file rtsig-max can be used to tune the maximum number
195 of POSIX realtime (queued) signals that can be outstanding
198 Rtsig-nr shows the number of RT signals currently queued.
200 ==============================================================
204 This file shows the size of the generic SCSI (sg) buffer.
205 You can't tune it just yet, but you could change it on
206 compile time by editing include/scsi/sg.h and changing
207 the value of SG_BIG_BUFF.
209 There shouldn't be any reason to change this value. If
210 you can come up with one, you probably know what you
213 ==============================================================
217 This value can be used to query and set the run time limit
218 on the maximum shared memory segment size that can be created.
219 Shared memory segments up to 1Gb are now supported in the
220 kernel. This value defaults to SHMMAX.
222 ==============================================================
226 Non-zero if the kernel has been tainted. Numeric values, which
227 can be ORed together:
229 1 - A module with a non-GPL license has been loaded, this
230 includes modules with no license.
231 Set by modutils >= 2.4.9.
232 2 - A module was force loaded by insmod -f.
233 Set by modutils >= 2.4.9.
235 ==============================================================
237 zero-paged: (PPC only)
239 When enabled (non-zero), Linux-PPC will pre-zero pages in
240 the idle loop, possibly speeding up get_free_pages. Since
241 this only affects what the idle loop is doing, you should
242 enable this and see if anything changes.