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 value in file-max denotes the maximum number of file- 92handles that the Linux kernel will allocate. When you get lots 93of error messages about running out of file handles, you might 94want to increase this limit. 95 96Historically,the kernel was able to allocate file handles 97dynamically, but not to free them again. The three values in 98file-nr denote the number of allocated file handles, the number 99of allocated but unused file handles, and the maximum number of 100file handles. Linux 2.6 always reports 0 as the number of free 101file handles -- this is not an error, it just means that the 102number of allocated file handles exactly matches the number of 103used file handles. 104 105Attempts to allocate more file descriptors than file-max are 106reported with printk, look for "VFS: file-max limit <number> 107reached". 108============================================================== 109 110nr_open: 111 112This denotes the maximum number of file-handles a process can 113allocate. Default value is 1024*1024 (1048576) which should be 114enough for most machines. Actual limit depends on RLIMIT_NOFILE 115resource limit. 116 117============================================================== 118 119inode-max, inode-nr & inode-state: 120 121As with file handles, the kernel allocates the inode structures 122dynamically, but can't free them yet. 123 124The value in inode-max denotes the maximum number of inode 125handlers. This value should be 3-4 times larger than the value 126in file-max, since stdin, stdout and network sockets also 127need an inode struct to handle them. When you regularly run 128out of inodes, you need to increase this value. 129 130The file inode-nr contains the first two items from 131inode-state, so we'll skip to that file... 132 133Inode-state contains three actual numbers and four dummies. 134The actual numbers are, in order of appearance, nr_inodes, 135nr_free_inodes and preshrink. 136 137Nr_inodes stands for the number of inodes the system has 138allocated, this can be slightly more than inode-max because 139Linux allocates them one pageful at a time. 140 141Nr_free_inodes represents the number of free inodes (?) and 142preshrink is nonzero when the nr_inodes > inode-max and the 143system needs to prune the inode list instead of allocating 144more. 145 146============================================================== 147 148overflowgid & overflowuid: 149 150Some filesystems only support 16-bit UIDs and GIDs, although in Linux 151UIDs and GIDs are 32 bits. When one of these filesystems is mounted 152with writes enabled, any UID or GID that would exceed 65535 is translated 153to a fixed value before being written to disk. 154 155These sysctls allow you to change the value of the fixed UID and GID. 156The default is 65534. 157 158============================================================== 159 160suid_dumpable: 161 162This value can be used to query and set the core dump mode for setuid 163or otherwise protected/tainted binaries. The modes are 164 1650 - (default) - traditional behaviour. Any process which has changed 166 privilege levels or is execute only will not be dumped 1671 - (debug) - all processes dump core when possible. The core dump is 168 owned by the current user and no security is applied. This is 169 intended for system debugging situations only. Ptrace is unchecked. 1702 - (suidsafe) - any binary which normally would not be dumped is dumped 171 readable by root only. This allows the end user to remove 172 such a dump but not access it directly. For security reasons 173 core dumps in this mode will not overwrite one another or 174 other files. This mode is appropriate when administrators are 175 attempting to debug problems in a normal environment. 176 177============================================================== 178 179super-max & super-nr: 180 181These numbers control the maximum number of superblocks, and 182thus the maximum number of mounted filesystems the kernel 183can have. You only need to increase super-max if you need to 184mount more filesystems than the current value in super-max 185allows you to. 186 187============================================================== 188 189aio-nr & aio-max-nr: 190 191aio-nr shows the current system-wide number of asynchronous io 192requests. aio-max-nr allows you to change the maximum value 193aio-nr can grow to. 194 195============================================================== 196 197 1982. /proc/sys/fs/binfmt_misc 199---------------------------------------------------------- 200 201Documentation for the files in /proc/sys/fs/binfmt_misc is 202in Documentation/binfmt_misc.txt. 203 204 2053. /proc/sys/fs/mqueue - POSIX message queues filesystem 206---------------------------------------------------------- 207 208The "mqueue" filesystem provides the necessary kernel features to enable the 209creation of a user space library that implements the POSIX message queues 210API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System 211Interfaces specification.) 212 213The "mqueue" filesystem contains values for determining/setting the amount of 214resources used by the file system. 215 216/proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the 217maximum number of message queues allowed on the system. 218 219/proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the 220maximum number of messages in a queue value. In fact it is the limiting value 221for another (user) limit which is set in mq_open invocation. This attribute of 222a queue must be less or equal then msg_max. 223 224/proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the 225maximum message size value (it is every message queue's attribute set during 226its creation). 227 228 2294. /proc/sys/fs/epoll - Configuration options for the epoll interface 230-------------------------------------------------------- 231 232This directory contains configuration options for the epoll(7) interface. 233 234max_user_watches 235---------------- 236 237Every epoll file descriptor can store a number of files to be monitored 238for event readiness. Each one of these monitored files constitutes a "watch". 239This configuration option sets the maximum number of "watches" that are 240allowed for each user. 241Each "watch" costs roughly 90 bytes on a 32bit kernel, and roughly 160 bytes 242on a 64bit one. 243The current default value for max_user_watches is the 1/32 of the available 244low memory, divided for the "watch" cost in bytes. 245 246