Documentation / sysctl / fs.txt
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Based on kernel version 3.4. Page generated on 2012-05-21 22:12 EST.
1 Documentation 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 5 For general info and legal blurb, please look in README. 6 7 ============================================================== 8 9 This file contains documentation for the sysctl files in 10 /proc/sys/fs/ and is valid for Linux kernel version 2.2. 11 12 The files in this directory can be used to tune and monitor 13 miscellaneous and general things in the operation of the Linux 14 kernel. Since some of the files _can_ be used to screw up your 15 system, it is advisable to read both documentation and source 16 before actually making adjustments. 17 18 1. /proc/sys/fs 19 ---------------------------------------------------------- 20 21 Currently, 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 41 aio-nr & aio-max-nr: 42 43 aio-nr is the running total of the number of events specified on the 44 io_setup system call for all currently active aio contexts. If aio-nr 45 reaches aio-max-nr then io_setup will fail with EAGAIN. Note that 46 raising aio-max-nr does not result in the pre-allocation or re-sizing 47 of any kernel data structures. 48 49 ============================================================== 50 51 dentry-state: 52 53 From linux/fs/dentry.c: 54 -------------------------------------------------------------- 55 struct { 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 64 Dentries are dynamically allocated and deallocated, and 65 nr_dentry seems to be 0 all the time. Hence it's safe to 66 assume that only nr_unused, age_limit and want_pages are 67 used. Nr_unused seems to be exactly what its name says. 68 Age_limit is the age in seconds after which dcache entries 69 can be reclaimed when memory is short and want_pages is 70 nonzero when shrink_dcache_pages() has been called and the 71 dcache isn't pruned yet. 72 73 ============================================================== 74 75 dquot-max & dquot-nr: 76 77 The file dquot-max shows the maximum number of cached disk 78 quota entries. 79 80 The file dquot-nr shows the number of allocated disk quota 81 entries and the number of free disk quota entries. 82 83 If the number of free cached disk quotas is very low and 84 you have some awesome number of simultaneous system users, 85 you might want to raise the limit. 86 87 ============================================================== 88 89 file-max & file-nr: 90 91 The value in file-max denotes the maximum number of file- 92 handles that the Linux kernel will allocate. When you get lots 93 of error messages about running out of file handles, you might 94 want to increase this limit. 95 96 Historically,the kernel was able to allocate file handles 97 dynamically, but not to free them again. The three values in 98 file-nr denote the number of allocated file handles, the number 99 of allocated but unused file handles, and the maximum number of 100 file handles. Linux 2.6 always reports 0 as the number of free 101 file handles -- this is not an error, it just means that the 102 number of allocated file handles exactly matches the number of 103 used file handles. 104 105 Attempts to allocate more file descriptors than file-max are 106 reported with printk, look for "VFS: file-max limit <number> 107 reached". 108 ============================================================== 109 110 nr_open: 111 112 This denotes the maximum number of file-handles a process can 113 allocate. Default value is 1024*1024 (1048576) which should be 114 enough for most machines. Actual limit depends on RLIMIT_NOFILE 115 resource limit. 116 117 ============================================================== 118 119 inode-max, inode-nr & inode-state: 120 121 As with file handles, the kernel allocates the inode structures 122 dynamically, but can't free them yet. 123 124 The value in inode-max denotes the maximum number of inode 125 handlers. This value should be 3-4 times larger than the value 126 in file-max, since stdin, stdout and network sockets also 127 need an inode struct to handle them. When you regularly run 128 out of inodes, you need to increase this value. 129 130 The file inode-nr contains the first two items from 131 inode-state, so we'll skip to that file... 132 133 Inode-state contains three actual numbers and four dummies. 134 The actual numbers are, in order of appearance, nr_inodes, 135 nr_free_inodes and preshrink. 136 137 Nr_inodes stands for the number of inodes the system has 138 allocated, this can be slightly more than inode-max because 139 Linux allocates them one pageful at a time. 140 141 Nr_free_inodes represents the number of free inodes (?) and 142 preshrink is nonzero when the nr_inodes > inode-max and the 143 system needs to prune the inode list instead of allocating 144 more. 145 146 ============================================================== 147 148 overflowgid & overflowuid: 149 150 Some filesystems only support 16-bit UIDs and GIDs, although in Linux 151 UIDs and GIDs are 32 bits. When one of these filesystems is mounted 152 with writes enabled, any UID or GID that would exceed 65535 is translated 153 to a fixed value before being written to disk. 154 155 These sysctls allow you to change the value of the fixed UID and GID. 156 The default is 65534. 157 158 ============================================================== 159 160 suid_dumpable: 161 162 This value can be used to query and set the core dump mode for setuid 163 or otherwise protected/tainted binaries. The modes are 164 165 0 - (default) - traditional behaviour. Any process which has changed 166 privilege levels or is execute only will not be dumped 167 1 - (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. 170 2 - (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 ============================================================== 178 179 super-max & super-nr: 180 181 These numbers control the maximum number of superblocks, and 182 thus the maximum number of mounted filesystems the kernel 183 can have. You only need to increase super-max if you need to 184 mount more filesystems than the current value in super-max 185 allows you to. 186 187 ============================================================== 188 189 aio-nr & aio-max-nr: 190 191 aio-nr shows the current system-wide number of asynchronous io 192 requests. aio-max-nr allows you to change the maximum value 193 aio-nr can grow to. 194 195 ============================================================== 196 197 198 2. /proc/sys/fs/binfmt_misc 199 ---------------------------------------------------------- 200 201 Documentation for the files in /proc/sys/fs/binfmt_misc is 202 in Documentation/binfmt_misc.txt. 203 204 205 3. /proc/sys/fs/mqueue - POSIX message queues filesystem 206 ---------------------------------------------------------- 207 208 The "mqueue" filesystem provides the necessary kernel features to enable the 209 creation of a user space library that implements the POSIX message queues 210 API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System 211 Interfaces specification.) 212 213 The "mqueue" filesystem contains values for determining/setting the amount of 214 resources used by the file system. 215 216 /proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the 217 maximum 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 220 maximum number of messages in a queue value. In fact it is the limiting value 221 for another (user) limit which is set in mq_open invocation. This attribute of 222 a 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 225 maximum message size value (it is every message queue's attribute set during 226 its creation). 227 228 229 4. /proc/sys/fs/epoll - Configuration options for the epoll interface 230 -------------------------------------------------------- 231 232 This directory contains configuration options for the epoll(7) interface. 233 234 max_user_watches 235 ---------------- 236 237 Every epoll file descriptor can store a number of files to be monitored 238 for event readiness. Each one of these monitored files constitutes a "watch". 239 This configuration option sets the maximum number of "watches" that are 240 allowed for each user. 241 Each "watch" costs roughly 90 bytes on a 32bit kernel, and roughly 160 bytes 242 on a 64bit one. 243 The current default value for max_user_watches is the 1/32 of the available 244 low memory, divided for the "watch" cost in bytes.
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