1Documentation for /proc/sys/fs/* kernel version 2.2.10 2 (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> 3 4For general info and legal blurb, please look in README. 5 6============================================================== 7 8This file contains documentation for the sysctl files in 9/proc/sys/fs/ and is valid for Linux kernel version 2.2. 10 11The files in this directory can be used to tune and monitor 12miscellaneous and general things in the operation of the Linux 13kernel. Since some of the files _can_ be used to screw up your 14system, it is advisable to read both documentation and source 15before actually making adjustments. 16 17Currently, these files are in /proc/sys/fs: 18- dentry-state 19- dquot-max 20- dquot-nr 21- file-max 22- file-nr 23- inode-max 24- inode-nr 25- inode-state 26- overflowuid 27- overflowgid 28- suid_dumpable 29- super-max 30- super-nr 31 32Documentation for the files in /proc/sys/fs/binfmt_misc is 33in Documentation/binfmt_misc.txt. 34 35============================================================== 36 37dentry-state: 38 39From linux/fs/dentry.c: 40-------------------------------------------------------------- 41struct { 42 int nr_dentry; 43 int nr_unused; 44 int age_limit; /* age in seconds */ 45 int want_pages; /* pages requested by system */ 46 int dummy[2]; 47} dentry_stat = {0, 0, 45, 0,}; 48-------------------------------------------------------------- 49 50Dentries are dynamically allocated and deallocated, and 51nr_dentry seems to be 0 all the time. Hence it's safe to 52assume that only nr_unused, age_limit and want_pages are 53used. Nr_unused seems to be exactly what its name says. 54Age_limit is the age in seconds after which dcache entries 55can be reclaimed when memory is short and want_pages is 56nonzero when shrink_dcache_pages() has been called and the 57dcache isn't pruned yet. 58 59============================================================== 60 61dquot-max & dquot-nr: 62 63The file dquot-max shows the maximum number of cached disk 64quota entries. 65 66The file dquot-nr shows the number of allocated disk quota 67entries and the number of free disk quota entries. 68 69If the number of free cached disk quotas is very low and 70you have some awesome number of simultaneous system users, 71you might want to raise the limit. 72 73============================================================== 74 75file-max & file-nr: 76 77The kernel allocates file handles dynamically, but as yet it 78doesn't free them again. 79 80The value in file-max denotes the maximum number of file- 81handles that the Linux kernel will allocate. When you get lots 82of error messages about running out of file handles, you might 83want to increase this limit. 84 85The three values in file-nr denote the number of allocated 86file handles, the number of unused file handles and the maximum 87number of file handles. When the allocated file handles come 88close to the maximum, but the number of unused file handles is 89significantly greater than 0, you've encountered a peak in your 90usage of file handles and you don't need to increase the maximum. 91 92============================================================== 93 94inode-max, inode-nr & inode-state: 95 96As with file handles, the kernel allocates the inode structures 97dynamically, but can't free them yet. 98 99The value in inode-max denotes the maximum number of inode 100handlers. This value should be 3-4 times larger than the value 101in file-max, since stdin, stdout and network sockets also 102need an inode struct to handle them. When you regularly run 103out of inodes, you need to increase this value. 104 105The file inode-nr contains the first two items from 106inode-state, so we'll skip to that file... 107 108Inode-state contains three actual numbers and four dummies. 109The actual numbers are, in order of appearance, nr_inodes, 110nr_free_inodes and preshrink. 111 112Nr_inodes stands for the number of inodes the system has 113allocated, this can be slightly more than inode-max because 114Linux allocates them one pageful at a time. 115 116Nr_free_inodes represents the number of free inodes (?) and 117preshrink is nonzero when the nr_inodes > inode-max and the 118system needs to prune the inode list instead of allocating 119more. 120 121============================================================== 122 123overflowgid & overflowuid: 124 125Some filesystems only support 16-bit UIDs and GIDs, although in Linux 126UIDs and GIDs are 32 bits. When one of these filesystems is mounted 127with writes enabled, any UID or GID that would exceed 65535 is translated 128to a fixed value before being written to disk. 129 130These sysctls allow you to change the value of the fixed UID and GID. 131The default is 65534. 132 133============================================================== 134 135suid_dumpable: 136 137This value can be used to query and set the core dump mode for setuid 138or otherwise protected/tainted binaries. The modes are 139 1400 - (default) - traditional behaviour. Any process which has changed 141 privilege levels or is execute only will not be dumped 1421 - (debug) - all processes dump core when possible. The core dump is 143 owned by the current user and no security is applied. This is 144 intended for system debugging situations only. Ptrace is unchecked. 1452 - (suidsafe) - any binary which normally would not be dumped is dumped 146 readable by root only. This allows the end user to remove 147 such a dump but not access it directly. For security reasons 148 core dumps in this mode will not overwrite one another or 149 other files. This mode is appropriate when administrators are 150 attempting to debug problems in a normal environment. 151 152============================================================== 153 154super-max & super-nr: 155 156These numbers control the maximum number of superblocks, and 157thus the maximum number of mounted filesystems the kernel 158can have. You only need to increase super-max if you need to 159mount more filesystems than the current value in super-max 160allows you to. 161 162============================================================== 163 164aio-nr & aio-max-nr: 165 166aio-nr shows the current system-wide number of asynchronous io 167requests. aio-max-nr allows you to change the maximum value 168aio-nr can grow to. 169 170============================================================== 171