file system ("Change mode") The Unix command and systemcall to change the access permissions of a named file.

Each file (directory, device, etc.) has nine kinds of access

which can be allowed or denied. Different permissions apply

to the owner of the file, the members of the group the file

belongs to, and all users. Each of these classes of user

(owner, group and other) can have permission to read, write or

execute the file. Chmod can also set various other mode bits

for a file or directory such as the sticky bit and the setuser id bit.