CHMOD(1) BSD Reference Manual CHMOD(1)
chmod - change file modes
chmod [-R [-H | -L | -P]] [-h] mode [file ...]
The chmod utility modifies the file mode bits of the listed files as
specified by the mode operand. The mode of a file dictates its permis-
sions, among other attributes.
The options are as follows:
-R Recursively descend through any specified directory arguments.
Change the modes of the file hierarchies rooted in the files in-
stead of just the files themselves.
-H If the -R option is also specified, symbolic links on the command
line are followed. (Symbolic links encountered in the tree
traversal are not followed.)
-L If the -R option is also specified, all symbolic links are fol-
lowed.
-P If the -R option is also specified, no symbolic links are fol-
lowed.
-h If file is symbolic link, the mode of the link is changed.
The -H, -L, and -P options are ignored unless the -R option is specified.
In addition, these options override each other and the command's actions
are determined by the last one specified.
Only the file's owner or the superuser is permitted to change the mode of
a file.
The chmod utility exits 0 on success or >0 if an error occurred.
Absolute modes are specified according to the following format:
chmod nnnn file [...]
An absolute mode is an octal number (specified as nnnn, where n is a
number from 0 to 7) constructed by ORing any of the following values:
0400 Allow read by owner.
0200 Allow write by owner.
0100 Allow execution (or search in directories) by owner.
0700 Allow read, write, and execute/search by owner.
0040 Allow read by group.
0020 Allow write by group.
0010 Allow execution (or search in directories) by group.
0070 Allow read, write, and execute/search by group.
0004 Allow read by others.
0002 Allow write by others.
0001 Allow execution (or search in directories) by others.
0007 Allow read, write, and execute/search by others.
In addition to the file permission modes, the following mode bits are
available:
4000 Set-user-ID on execution.
2000 Set-group-ID on execution.
1000 Enable sticky bit; see sticky(7) and chmod(2).
The execute bit for a directory is often referred to as the "search" bit.
In order to access a file, a user must have execute permission in each
directory leading up to it in the filesystem hierarchy. For example, to
access the file /bin/ls, execute permission is needed on /, /bin, and, of
course, the ls binary itself.
Symbolic modes are specified according to the following format:
chmod <[who]op[perm]>,[[who]op[perm]],[...] file [...]
The symbolic mode is described by the following grammar:
mode ::= clause [, clause ...]
clause ::= [who ...] [action ...] last_action
action ::= op [perm ...]
last_action ::= op [perm ...]
who ::= a | u | g | o
op ::= + | - | =
perm ::= r | s | t | w | x | X | u | g | o
The who symbols indicate whose permissions are to be changed or assigned:
u User (owner) permissions.
g Group permissions.
o Others permissions.
a All of the above.
Do not confuse the 'o' symbol with "owner". It is the user bit, 'u', that
refers to the owner of the file.
The op symbols represent the operation performed, as follows:
+ If no value is supplied for perm, the '+' operation has no
effect. If no value is supplied for who, each permission bit
specified in perm, for which the corresponding bit in the
file mode creation mask is clear, is set. Otherwise, the mode
bits represented by the specified who and perm values are
set.
- If no value is supplied for perm, the '-' operation has no
effect. If no value is supplied for who, each permission bit
specified in perm, for which the corresponding bit in the
file mode creation mask is clear, is cleared. Otherwise, the
mode bits represented by the specified who and perm values
are cleared.
= The mode bits specified by the who value are cleared, or, if
no who value is specified, the user, group and other mode
bits are cleared. Then, if no value is supplied for who, each
permission bit specified in perm, for which the corresponding
bit in the file mode creation mask is clear, is set. Other-
wise, the mode bits represented by the specified who and perm
values are set.
The perm (permission symbols) represent the portions of the mode bits as
follows:
r Read bits.
s Set-user-ID and set-group-ID on execution bits.
t Sticky bit.
w Write bits.
x Execute/search bits.
X The execute/search bits if the file is a directory or any
of the execute/search bits are set in the original (unmodi-
fied) mode. Operations with the perm symbol 'X' are only
meaningful in conjunction with the op symbol '+', and are
ignored in all other cases.
u User permission bits in the mode of the original file.
g Group permission bits in the mode of the original file.
o Other permission bits in the mode of the original file.
Each clause (given in a comma-delimited list on the command line) speci-
fies one or more operations to be performed on the mode bits, and each
operation is applied in the order specified.
Operations upon the "other" permissions (specified by the symbol 'o' by
itself), in combination with the perm symbols 's' or 't', are ignored.
$ chmod 644 file
Set file readable by anyone and writable by the owner only.
$ chmod go-w file
Deny write permission to group and others.
$ chmod =rw,+X file
Set the read and write permissions to the usual defaults, but retain any
execute permissions that are currently set.
$ chmod +X file
Make a directory or file searchable/executable by everyone if it is al-
ready searchable/executable by anyone.
$ chmod 755 file
$ chmod u=rwx,go=rx file
$ chmod u=rwx,go=u-w file
Any of these commands will make a file readable/executable by everyone
and writable by the owner only.
$ chmod go= file
Clear all mode bits for group and others.
$ chmod g=u-w file
Set the group bits equal to the user bits, but clear the group write bit.
chflags(1), chgrp(1), find(1), install(1), chmod(2), lchmod(2), stat(2),
umask(2), fts(3), setmode(3), sticky(7), symlink(7), chown(8)
The chmod utility is expected to be IEEE Std 1003.2 ("POSIX.2") compati-
ble with the exception of the perm symbols 't' and 'X' which are not in-
cluded in that standard.
A chmod command appeared in Version 1 AT&T UNIX. The -h option appeared
in MirBSD #10.
There's no perm option for the naughty bits.
MirBSD #10-current April 14, 2020 2