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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
Eric Dumazet9cfe0152008-02-06 01:37:16 -080026- nr_open
Linus Torvalds1da177e2005-04-16 15:20:36 -070027- overflowuid
28- overflowgid
Alexey Dobriyana2e0b562006-08-27 01:23:28 -070029- suid_dumpable
Linus Torvalds1da177e2005-04-16 15:20:36 -070030- super-max
31- super-nr
32
33Documentation for the files in /proc/sys/fs/binfmt_misc is
34in Documentation/binfmt_misc.txt.
35
36==============================================================
37
38dentry-state:
39
40From linux/fs/dentry.c:
41--------------------------------------------------------------
42struct {
43 int nr_dentry;
44 int nr_unused;
45 int age_limit; /* age in seconds */
46 int want_pages; /* pages requested by system */
47 int dummy[2];
48} dentry_stat = {0, 0, 45, 0,};
49--------------------------------------------------------------
50
51Dentries are dynamically allocated and deallocated, and
52nr_dentry seems to be 0 all the time. Hence it's safe to
53assume that only nr_unused, age_limit and want_pages are
54used. Nr_unused seems to be exactly what its name says.
55Age_limit is the age in seconds after which dcache entries
56can be reclaimed when memory is short and want_pages is
57nonzero when shrink_dcache_pages() has been called and the
58dcache isn't pruned yet.
59
60==============================================================
61
62dquot-max & dquot-nr:
63
64The file dquot-max shows the maximum number of cached disk
65quota entries.
66
67The file dquot-nr shows the number of allocated disk quota
68entries and the number of free disk quota entries.
69
70If the number of free cached disk quotas is very low and
71you have some awesome number of simultaneous system users,
72you might want to raise the limit.
73
74==============================================================
75
76file-max & file-nr:
77
78The kernel allocates file handles dynamically, but as yet it
79doesn't free them again.
80
81The value in file-max denotes the maximum number of file-
82handles that the Linux kernel will allocate. When you get lots
83of error messages about running out of file handles, you might
84want to increase this limit.
85
86The three values in file-nr denote the number of allocated
87file handles, the number of unused file handles and the maximum
88number of file handles. When the allocated file handles come
89close to the maximum, but the number of unused file handles is
90significantly greater than 0, you've encountered a peak in your
91usage of file handles and you don't need to increase the maximum.
92
93==============================================================
94
Eric Dumazet9cfe0152008-02-06 01:37:16 -080095nr_open:
96
97This denotes the maximum number of file-handles a process can
98allocate. Default value is 1024*1024 (1048576) which should be
99enough for most machines. Actual limit depends on RLIMIT_NOFILE
100resource limit.
101
102==============================================================
103
Linus Torvalds1da177e2005-04-16 15:20:36 -0700104inode-max, inode-nr & inode-state:
105
106As with file handles, the kernel allocates the inode structures
107dynamically, but can't free them yet.
108
109The value in inode-max denotes the maximum number of inode
110handlers. This value should be 3-4 times larger than the value
111in file-max, since stdin, stdout and network sockets also
112need an inode struct to handle them. When you regularly run
113out of inodes, you need to increase this value.
114
115The file inode-nr contains the first two items from
116inode-state, so we'll skip to that file...
117
118Inode-state contains three actual numbers and four dummies.
119The actual numbers are, in order of appearance, nr_inodes,
120nr_free_inodes and preshrink.
121
122Nr_inodes stands for the number of inodes the system has
123allocated, this can be slightly more than inode-max because
124Linux allocates them one pageful at a time.
125
126Nr_free_inodes represents the number of free inodes (?) and
127preshrink is nonzero when the nr_inodes > inode-max and the
128system needs to prune the inode list instead of allocating
129more.
130
131==============================================================
132
133overflowgid & overflowuid:
134
135Some filesystems only support 16-bit UIDs and GIDs, although in Linux
136UIDs and GIDs are 32 bits. When one of these filesystems is mounted
137with writes enabled, any UID or GID that would exceed 65535 is translated
138to a fixed value before being written to disk.
139
140These sysctls allow you to change the value of the fixed UID and GID.
141The default is 65534.
142
143==============================================================
144
Alexey Dobriyana2e0b562006-08-27 01:23:28 -0700145suid_dumpable:
146
147This value can be used to query and set the core dump mode for setuid
148or otherwise protected/tainted binaries. The modes are
149
1500 - (default) - traditional behaviour. Any process which has changed
151 privilege levels or is execute only will not be dumped
1521 - (debug) - all processes dump core when possible. The core dump is
153 owned by the current user and no security is applied. This is
154 intended for system debugging situations only. Ptrace is unchecked.
1552 - (suidsafe) - any binary which normally would not be dumped is dumped
156 readable by root only. This allows the end user to remove
157 such a dump but not access it directly. For security reasons
158 core dumps in this mode will not overwrite one another or
Matt LaPlante5d3f0832006-11-30 05:21:10 +0100159 other files. This mode is appropriate when administrators are
Alexey Dobriyana2e0b562006-08-27 01:23:28 -0700160 attempting to debug problems in a normal environment.
161
162==============================================================
163
Linus Torvalds1da177e2005-04-16 15:20:36 -0700164super-max & super-nr:
165
166These numbers control the maximum number of superblocks, and
167thus the maximum number of mounted filesystems the kernel
168can have. You only need to increase super-max if you need to
169mount more filesystems than the current value in super-max
170allows you to.
171
172==============================================================
173
174aio-nr & aio-max-nr:
175
176aio-nr shows the current system-wide number of asynchronous io
177requests. aio-max-nr allows you to change the maximum value
178aio-nr can grow to.
179
180==============================================================