The umask value is subtracted from these default permissions after the function has created the new file or directory. Thus, a directory will have permissions of 775 by default, a file 664 , if the mask value is (0)002 . This is demonstrated in the example below:
bert:~> mkdir newdir
bert:~> ls -ld newdir
drwxrwxr-x 2 bert bert 4096 Feb 28 13:45 newdir/
bert:~> touch newfile
bert:~> ls -l newfile
-rw-rw-r-- 1 bert bert 0 Feb 28 13:52 newfile
If you log in to another group using the newgrp command, the mask remains unchanged. Thus, if it is set to 002 , files and directories that you create while being in the new group will also be accessible to the other members of that group; you don't have to use chmod .
The root user usually has stricter default file creation permissions:
[root@estoban root]# umask
022
These defaults are set system-wide in the shell resource configuration files, for instance /etc/bashrc or /etc/profile . You can change them in your own shell configuration file, see Chapter 7 on customizing your shell environment.
3.4.2.4. Changing user and group ownership
When a file is owned by the wrong user or group, the error can be repaired with the chown (change owner) and chgrp (change group) commands. Changing file ownership is a frequent system administrative task in environments where files need to be shared in a group. Both commands are very flexible, as you can find out by using the --help option.
The chown command can be applied to change both user and group ownership of a file, while chgrp only changes group ownership. Of course the system will check if the user issuing one of these commands has sufficient permissions on the file(s) she wants to change.
In order to only change the user ownership of a file, use this syntax:
chown newuser file
If you use a colon after the user name (see the Info pages), group ownership will be changed as well, to the primary group of the user issuing the command. On a Linux system, each user has his own group, so this form can be used to make files private:
jacky:~> id
uid=1304(jacky) gid=(1304) groups=1304(jacky),2034(pproject)
jacky:~> ls -l my_report
-rw-rw-r-- 1 jacky project 29387 Jan 15 09:34 my_report
jacky:~> chown jacky: my_report
jacky:~> chmod o-r my_report
jacky:~> ls -l my_report
-rw-rw---- 1 jacky jacky 29387 Jan 15 09:34 my_report
If jacky would like to share this file, without having to give everybody permission to write it, he can use the chgrp command:
jacky:~> ls -l report-20020115.xls
-rw-rw---- 1 jacky jacky 45635 Jan 15 09:35 report-20020115.xls
jacky:~> chgrp project report-20020115.xls
jacky:~> chmod o= report-20020115.xls
jacky:~> ls -l report-20020115.xls
-rw-rw---- 1 jacky project 45635 Jan 15 09:35 report-20020115.xls
This way, users in the group project will be able to work on this file. Users not in this group have no business with it at all.
Both chown and chgrp can be used to change ownership
