User File Permissions

System Users and Permissions

All files within a Linux system define permissions for owner, group, and others.

The available permissions for any given owner, group, and other users is as follows:

• Read
• Write
• Execute
• None

An owner, group, or other users can have any combination of the above permissions.

The following list shows all possible options:

• Read only
• Write only
• Execute only
• Read and Write
• Read and Execute
• Write and Execute
• Read, Write, and Execute
• None

Viewing Permissions in Terminal

Open up a terminal and navigate to the home directory if necessary.

View all the contents of the home directory with:

ls -l

For each non hidden file found by ls -l the following is displayed:

• file type
• file permissions
• number of contained folders
• file owner
• file group
• file size (in bytes)
• file last touched date
• file name

Output:

The line with the Desktop directory can be broken down as follows:

• file type: d for directory
• file permissions: rwxr-xr-x
• number of contained files: 4
• file owner: student
• file group: student
• file size (in bytes): 4096 bytes (4 kilobytes)
• file last touched date: Apr 20 10:00
• file name: Desktop

The file permissions section defines read, write and execute permissions for each of the file owner, file group, and all other users.

rwxr-xr-x is broken into three:

• rwx: the file owner has read, write and execute permissions
• r-x: the file group has read and execute permissions
• r-x: all other users have read and execute permissions

Bringing it together:

• drwxr-xr-x 4 student student:
  • Directory that allows the student user to Read, Write, and Execute, the student group to Execute and Read, and all others to Execute only.

The line with the snap directory is as follows:

• drwx------ 4 student student:
  • Directory that allows the student owner to Read, Write, and Execute, the student group has None permissions, and all other users have None permissions.

Alternate Users

Now that you have a basic understanding of the user and file permissions structure lets take a look at a different directory with alternate users.

Using the ls -l command view the file permissions for all files within the root directory:

ls -l /

Output:

Take note that all folders and files located within the root directory belong to the root user and root group.

/usr/ File Permission Breakdown

drwxr-xr-x  21 root root        4096 Apr 20 10:20 tmp

drwxr-xr-x:

• d: file is of the directory type
• rwx: root owner has read, write and execute privileges
• r-x: root group has read and execute privileges
• r-x: all other users have read and execute privileges

/lost+found/ File Permission Breakdown

drwx------  2 root root        16384 Mar 11 14:32 lost+found

drwx------:

• d: file is of the directory type
• rwx: the root owner has read, write and execute privileges
• ---: the root group has no permissions
• ---: all other users have no permissions