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Linus Torvalds1da177e2005-04-16 15:20:36 -07001Documentation 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
Alexey Dobriyana2e0b562006-08-27 01:23:28 -070028- suid_dumpable
Linus Torvalds1da177e2005-04-16 15:20:36 -070029- 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
Alexey Dobriyana2e0b562006-08-27 01:23:28 -0700135suid_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
Matt LaPlante5d3f0832006-11-30 05:21:10 +0100149 other files. This mode is appropriate when administrators are
Alexey Dobriyana2e0b562006-08-27 01:23:28 -0700150 attempting to debug problems in a normal environment.
151
152==============================================================
153
Linus Torvalds1da177e2005-04-16 15:20:36 -0700154super-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==============================================================