chmod — stdin stdout - file -- opt --help --version
chmod (change mode)
command protects files and directories from unauthorized users on
the same system, by setting access permissions. Typical permissions
are read, write, and execute, and they may be limited to the file
owner, the file’s group owner, and/or other users. The permissions
argument can take three different forms:
file, to set the same permissions as
another given file.
An octal number, up to four digits long, that specifies the file’s absolute permissions in bits, as in Figure 1-6. The leftmost digit is special (described later) and the second, third, and fourth represent the file’s owner, the file’s group, and all users.
One or more strings specifying absolute or
relative permissions (i.e., relative to the file’s
existing permissions). For example,
a+r makes a file readable by all
Figure 1-6. File permission bits explained
In the third form, each string consists of three parts: an optional scope, a command, and permissions.
u for user,
g for group,
o for other users not in the group,
a for all users. The
+ to add permissions;
− to remove permissions; or
= to set absolute
permissions, ignoring existing ones.
r for read,
w for write/modify,
x for execute (for directories, this
is permission to
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