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Each user and group is assigned an identification number (UID or GID). This ID number is stamped on all files, directories, and processes on local and NFS-mounted filesystems. When you create a new user or group, a new UID or GID number is automatically generated, but you can specify another by entering it in the text field.
Change the ID number for an existing user with the
usermod(1M)
command. You can include -U option to change the users
files to the new UID, as in this example:
usermod -u 712 -U jstone
This command also changes any crontab files. The -U option changes the ownership of files found in directories specified in /etc/default/usermod; it does not locate all files owned by the user.
The groupmod(1M) performs similar functions for groups.
To alter the range of GIDs from which you select for new groups, select Options Group Defaults.
See also:
If you have changed or removed a UID or GID, you must change the ownership of files belonging to that ID and check your filesystems for orphaned files. Files without a real owner have a number in the owner and/or group name fields:
-rw-r--r-- 1 obie pub 68476 Nov 16 12:06 accts.s -rw-r--r-- 1 15625 pub 508 Oct 31 11:15 balance -rw-r--r-- 1 obie pub 40596 Aug 31 13:19 report.2In this example, the file balance is an orphaned file. The number appears because files are stamped with the ID number rather than the user or group name.
Use the
find(1)
utility to locate and change the ownership of files.
This command-line finds all files on the system owned by user
UID and changes ownership to user newowner:
find / -user UID -print | xargs -t chown newowner
This variation changes the group ownership:
find / -user GID -print | xargs -t chgrp newgroup
Instead of changing the ownership, you can perform other actions, such as archiving the files; see ``Locating files''.
See also: