Unix file system : Permissions

The file /etc/passwd is the password file. It contains all the login information about each user. We can discover each users id and group id by looking name in /etc/passwd.

$grep name /etc/passwd

The fields in the password file looks like ‘login-id:encrypted password:uid:group-id:miscellany:login-directory:shell’. The -l option of ls command prints the permissions.

$ls -l

We can find a string like ‘-rw-r–r–‘ . The first – means that it is an ordinary file. If it is a directory there prints a ‘d’. The next three field is the permissions of the owner followed by the next three field is the permissions of the group and the next is the others permissions. We cannot edit the passwd file . But the super user can do it.

The ‘chmod’ command changes the permissions of a file. ‘permissions’ may occupy octal numbers. The ‘+’ sign is for ‘ON’ permission modes and to OFF the ‘-‘ sign is using. The ‘-w’ option is for turn off the write permisssion for all incliding the owner. ‘+x’ allows every one to execute the following command.

$ chmod permissions filename
$ chmod -w filename
$ chmod +x command
$ chmod -w .
$ chmod 775 filename //Restores the permission.

The ‘-w .’ means removing the write permission of all files in that directory.

Advertisements

Author: Abhilash

Hi, this is Abhilash - Senior Programmer Analyst at CoMakeIT, specialised on web programming. Mainly working on Ruby On Rails platform since 2010.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s