1Documentation for /proc/sys/fs/* kernel version 2.2.10 2 (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> 3 (c) 2009, Shen Feng<shen@cn.fujitsu.com> 4 5For general info and legal blurb, please look in README. 6 7============================================================== 8 9This file contains documentation for the sysctl files in 10/proc/sys/fs/ and is valid for Linux kernel version 2.2. 11 12The files in this directory can be used to tune and monitor 13miscellaneous and general things in the operation of the Linux 14kernel. Since some of the files _can_ be used to screw up your 15system, it is advisable to read both documentation and source 16before actually making adjustments. 17 181. /proc/sys/fs 19---------------------------------------------------------- 20 21Currently, these files are in /proc/sys/fs: 22- aio-max-nr 23- aio-nr 24- dentry-state 25- dquot-max 26- dquot-nr 27- file-max 28- file-nr 29- inode-max 30- inode-nr 31- inode-state 32- nr_open 33- overflowuid 34- overflowgid 35- suid_dumpable 36- super-max 37- super-nr 38 39============================================================== 40 41aio-nr & aio-max-nr: 42 43aio-nr is the running total of the number of events specified on the 44io_setup system call for all currently active aio contexts. If aio-nr 45reaches aio-max-nr then io_setup will fail with EAGAIN. Note that 46raising aio-max-nr does not result in the pre-allocation or re-sizing 47of any kernel data structures. 48 49============================================================== 50 51dentry-state: 52 53From linux/fs/dentry.c: 54-------------------------------------------------------------- 55struct { 56 int nr_dentry; 57 int nr_unused; 58 int age_limit; /* age in seconds */ 59 int want_pages; /* pages requested by system */ 60 int dummy[2]; 61} dentry_stat = {0, 0, 45, 0,}; 62-------------------------------------------------------------- 63 64Dentries are dynamically allocated and deallocated, and 65nr_dentry seems to be 0 all the time. Hence it's safe to 66assume that only nr_unused, age_limit and want_pages are 67used. Nr_unused seems to be exactly what its name says. 68Age_limit is the age in seconds after which dcache entries 69can be reclaimed when memory is short and want_pages is 70nonzero when shrink_dcache_pages() has been called and the 71dcache isn't pruned yet. 72 73============================================================== 74 75dquot-max & dquot-nr: 76 77The file dquot-max shows the maximum number of cached disk 78quota entries. 79 80The file dquot-nr shows the number of allocated disk quota 81entries and the number of free disk quota entries. 82 83If the number of free cached disk quotas is very low and 84you have some awesome number of simultaneous system users, 85you might want to raise the limit. 86 87============================================================== 88 89file-max & file-nr: 90 91The kernel allocates file handles dynamically, but as yet it 92doesn't free them again. 93 94The value in file-max denotes the maximum number of file- 95handles that the Linux kernel will allocate. When you get lots 96of error messages about running out of file handles, you might 97want to increase this limit. 98 99The three values in file-nr denote the number of allocated 100file handles, the number of unused file handles and the maximum 101number of file handles. When the allocated file handles come 102close to the maximum, but the number of unused file handles is 103significantly greater than 0, you've encountered a peak in your 104usage of file handles and you don't need to increase the maximum. 105 106============================================================== 107 108nr_open: 109 110This denotes the maximum number of file-handles a process can 111allocate. Default value is 1024*1024 (1048576) which should be 112enough for most machines. Actual limit depends on RLIMIT_NOFILE 113resource limit. 114 115============================================================== 116 117inode-max, inode-nr & inode-state: 118 119As with file handles, the kernel allocates the inode structures 120dynamically, but can't free them yet. 121 122The value in inode-max denotes the maximum number of inode 123handlers. This value should be 3-4 times larger than the value 124in file-max, since stdin, stdout and network sockets also 125need an inode struct to handle them. When you regularly run 126out of inodes, you need to increase this value. 127 128The file inode-nr contains the first two items from 129inode-state, so we'll skip to that file... 130 131Inode-state contains three actual numbers and four dummies. 132The actual numbers are, in order of appearance, nr_inodes, 133nr_free_inodes and preshrink. 134 135Nr_inodes stands for the number of inodes the system has 136allocated, this can be slightly more than inode-max because 137Linux allocates them one pageful at a time. 138 139Nr_free_inodes represents the number of free inodes (?) and 140preshrink is nonzero when the nr_inodes > inode-max and the 141system needs to prune the inode list instead of allocating 142more. 143 144============================================================== 145 146overflowgid & overflowuid: 147 148Some filesystems only support 16-bit UIDs and GIDs, although in Linux 149UIDs and GIDs are 32 bits. When one of these filesystems is mounted 150with writes enabled, any UID or GID that would exceed 65535 is translated 151to a fixed value before being written to disk. 152 153These sysctls allow you to change the value of the fixed UID and GID. 154The default is 65534. 155 156============================================================== 157 158suid_dumpable: 159 160This value can be used to query and set the core dump mode for setuid 161or otherwise protected/tainted binaries. The modes are 162 1630 - (default) - traditional behaviour. Any process which has changed 164 privilege levels or is execute only will not be dumped 1651 - (debug) - all processes dump core when possible. The core dump is 166 owned by the current user and no security is applied. This is 167 intended for system debugging situations only. Ptrace is unchecked. 1682 - (suidsafe) - any binary which normally would not be dumped is dumped 169 readable by root only. This allows the end user to remove 170 such a dump but not access it directly. For security reasons 171 core dumps in this mode will not overwrite one another or 172 other files. This mode is appropriate when administrators are 173 attempting to debug problems in a normal environment. 174 175============================================================== 176 177super-max & super-nr: 178 179These numbers control the maximum number of superblocks, and 180thus the maximum number of mounted filesystems the kernel 181can have. You only need to increase super-max if you need to 182mount more filesystems than the current value in super-max 183allows you to. 184 185============================================================== 186 187aio-nr & aio-max-nr: 188 189aio-nr shows the current system-wide number of asynchronous io 190requests. aio-max-nr allows you to change the maximum value 191aio-nr can grow to. 192 193============================================================== 194 195 1962. /proc/sys/fs/binfmt_misc 197---------------------------------------------------------- 198 199Documentation for the files in /proc/sys/fs/binfmt_misc is 200in Documentation/binfmt_misc.txt. 201 202 2033. /proc/sys/fs/mqueue - POSIX message queues filesystem 204---------------------------------------------------------- 205 206The "mqueue" filesystem provides the necessary kernel features to enable the 207creation of a user space library that implements the POSIX message queues 208API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System 209Interfaces specification.) 210 211The "mqueue" filesystem contains values for determining/setting the amount of 212resources used by the file system. 213 214/proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the 215maximum number of message queues allowed on the system. 216 217/proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the 218maximum number of messages in a queue value. In fact it is the limiting value 219for another (user) limit which is set in mq_open invocation. This attribute of 220a queue must be less or equal then msg_max. 221 222/proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the 223maximum message size value (it is every message queue's attribute set during 224its creation). 225 226 2274. /proc/sys/fs/epoll - Configuration options for the epoll interface 228-------------------------------------------------------- 229 230This directory contains configuration options for the epoll(7) interface. 231 232max_user_instances 233------------------ 234 235This is the maximum number of epoll file descriptors that a single user can 236have open at a given time. The default value is 128, and should be enough 237for normal users. 238 239max_user_watches 240---------------- 241 242Every epoll file descriptor can store a number of files to be monitored 243for event readiness. Each one of these monitored files constitutes a "watch". 244This configuration option sets the maximum number of "watches" that are 245allowed for each user. 246Each "watch" costs roughly 90 bytes on a 32bit kernel, and roughly 160 bytes 247on a 64bit one. 248The current default value for max_user_watches is the 1/32 of the available 249low memory, divided for the "watch" cost in bytes. 250 251