chmod - change file mode
$ chmod <octal-mode> <path...>
$ chmod <mode> <path...>chmod changes mode of all files specified in path to octal-mode or using symbolic representation.
The symbolic representation format is [[ugoa][+-=][rwx...],...]. Multiple symbolic can be given, separated by commas.
The letters [ugoa] controls which users' access will be changes: u means file owner, g file owning group, o others, and a - all users. If no letter is given, a is assumed.
The letters [+-=] controls which action will be taken: + sets the permission, - removes the permission, and = sets the mentioned permissions and unsets the other permissions.
The letters [rwx] controls which permission will be changes: r is read, w is write and x is execute.
A numeric mode is combination of 1 to 4 numbers. Omitted digits are assumet to be leading zeros. The first digit select the set user ID (4), set group ID (2) and restricted deletion / sticky (1) attributes. The second, third and fourth digit controls permissions of each user group: owner, owning group and others (not owner or owning group), respectively: read (4), write (2) and execute (1).
# Allow full access for owner, read-execute for group, and no access for others, of 'README.md':
$ chmod 750 README.md
# Change '/bin/su' to be set-uid, read-write-execute for owner, only execute for others:
# chmod 4711 /bin/su
# Add read access for others to all files in 'Source' directory:
$ chmod o+r Source/*
# Deny read and write access for non-owners, and allow full access for owners of 'script.sh':
$ chmod o-rw,g-rw,u+rwx script.sh
# Set group access to only read of 'script.sh':
$ chmod g=r script.sh