Linux File Permissions and Management Guide
Learn how to control file access and manage accounts in Linux with our guide.
Explore file permissions, chmod, chown, management, and more
Linux file permissions are a crucial aspect of managing files and directories on a Unix-based system, like Linux.
They determine who can read, write, and execute a file or directory. Permissions are usually represented in the form of a 10-character string, where the first character represents the file type, and the remaining nine characters are divided into three groups of three, each representing the permission set for the owner, group, and others.
Here’s an introduction to some common Linux commands related to file permissions, along with code examples:
-rw-r–r– 1 1024 Nov 1 10:00 myfile.txt
drwxr-xr-x 2 4096 Nov 1 10:01 mydir
In the output, the file permissions are displayed as rw-r–r–, where the first character indicates the file type (‘-‘ for a regular file and ‘d’ for a directory), and the remaining nine characters represent the permissions.
chmod u+rw myfile.txt
chmod o-w myfile.txt
chmod 744 myfile.txt
chown new myfile.txt
chown :newgroup myfile.txt
chgrp newgroup myfile.txt
To set a default umask for a to allow read and write for themselves and read-only for others:
ls – List Files
List files and directories, displaying file permissions, ownership, and other details.
Modify file permissions using symbolic or octal notation.
Example (add read and write permissions for the owner):
chmod u+rw myfile.txt
Change the owner and/or group of a file or directory.
Example (change the owner of a file):
chown new myfile.txt
Change the group ownership of a file or directory.
Example (change the group of a file):
chgrp newgroup myfile.txt
Set default permissions for newly created files and directories.
Example (set a default umask):
Change a ‘s password.
Switch to another account with super privileges.
Example (switch to the root ):
Run a command with super (root) privileges.
Example (update system packages with sudo):
sudo apt update
Change ownership recursively for a directory and its contents.
Example (change owner and group recursively):
chown -R new:newgroup mydirectory/
Search for files and directories based on various criteria, including permissions.
Example (find files with specific permissions):
find /path/to/search -type f -perm 644
Display the current umask value, which controls default permissions for new files and directories.
Display the and group information for the current .
List the groups to which the current belongs.
Set access control lists (ACLs) for files and directories to provide fine-grained access control.
Example (add read permission for a specific ):
setfacl -m u:name:r myfile.txt
Display the access control lists (ACLs) for a file or directory.
Set the set group ID (SGID) on a directory to ensure new files inherit the group ownership of the directory.
chmod g+s mydirectory/
Set the sticky bit on a directory to restrict file deletion to the file owner.
chmod +t mydirectory/
Change the password for a group.
sudo passwd groupname
add – Add a New
sudo add new
del – Delete a
Delete a account and associated files from the system.
sudo del old
Modify account properties, including group membership and ID.
Example (add to a group):
sudo mod -aG newgroup new
Change file attributes to make files immutable or append-only.
Example (set a file as immutable):
chattr +i myfile.txt
These additional Linux commands provide more advanced options for managing file permissions, accounts, and access control on your system.
Use them as needed to meet your specific requirements and maintain the security and integrity of your files and directories.
Here are some more Linux commands related to file permissions and management:
Retrieve entries from various administrative databases, including and group information.
Example (get information):
getent passwd name
Set password expiration and aging information for a account.
Example (set password expiration date for a ):
chage -E 2024-12-31 name
Edit the sudoers file to configure sudo access and permissions for s and groups.
Example (edit the sudoers file):
Change the effective group ID for the current session.
Display the group memberships for a specific .
Set the set ID (SUID) on an executable file to run with the owner’s privileges.
chmod u+s myprogram
Lock a account to prevent login access.
sudo passwd -l name
passwd -u – Unlock Account
sudo passwd -u name
Set the ‘s shell to /usr/sbin/nologin to prevent login access.
sudo mod --shell /usr/sbin/nologin name
Change the effective and group by specifying them with the -u and -g options.
su -u new -g newgroup
Show information about s who are currently logged in.
These additional Linux commands offer various functionalities for managing accounts, access control, and security settings on your system. Use them as needed based on your specific requirements and system administration tasks.
Here’s a quiz about the Linux commands related to file permissions and management, along with the answers:
1-What command is used to list files and directories with their permissions, ownership, and other details?
Answer: b) ls
2-Which command is used to change file permissions?
Answer: c) chmod
3-How can you add read and write permissions for the owner of a file using chmod?
a) chmod u+rw myfile.txt
b) chmod o+rw myfile.txt
c) chmod g+rw myfile.txt
d) chmod a+rw myfile.txt
Answer: a) chmod u+rw myfile.txt
4-Which command is used to change the ownership of a file or directory?
Answer: b) chown
5-What is the purpose of the umask command in Linux?
a) Display current and group information.
b) Set the default permissions for newly created files and directories.
c) Change the password for a .
Answer: b) Set the default permissions for newly created files and directories.
6-Which command is used to set access control lists (ACLs) for files and directories in Linux?
Answer: c) setfacl
7-What does the sticky bit do when set on a directory in Linux?
a) Prevents the directory from being accessed by anyone.
b) Restricts file deletion to the file owner.
c) Allows anyone to modify files in the directory.
d) Enables read-only access for all s.
Answer: b) Restricts file deletion to the file owner.
8-Which command is used to edit the sudoers file and configure sudo access and permissions for s and groups?
Answer: b) visudo
9-How can you lock a account in Linux to prevent login access?
a) passwd -s lock name
b) lock -l name
c) passwd -l name
d) mod -l name
Answer: c) passwd -l name
10-Which command displays information about s who are currently logged in?
Answer: c) who
11-What is the purpose of the chgrp command in Linux?
a) Change the group password.
b) Change the owner of a file.
c) Change the group ownership of a file or directory.
d) Change the default permissions for new files.
Answer: c) Change the group ownership of a file or directory.
12-Which command allows you to set the set group ID (SGID) on a directory?
c) chmod g+s
Answer: c) chmod g+s
13-What is the purpose of the sticky bit on a directory in Linux?
a) Prevents the directory from being accessed.
b) Restricts file deletion to the directory owner.
c) Allows any to modify files in the directory.
d) Sets read-only access for all s.
Answer: b) Restricts file deletion to the directory owner.
14-Which command is used to get entries from administrative databases, including and group information?
Answer: a) getent
15-What is the purpose of the passwd -u command in Linux?
a) Set the password for a .
b) Unlock a previously locked
c) Set password expiration and aging information.
d) Change the default
Answer: b) Unlock a previously locked account.
16-Which command is used to display group memberships?
Answer: a) groups
17-What does the set ID (SUID) do when set on an executable file in Linux?
a) Allows execution by any .
b) Sets the ‘s identity to the file owner’s identity.
c) Gives execute permissions to the group.
d) Makes the file immutable.
Answer: b) Sets the ‘s identity to the file owner’s identity.
18-Which command is used to change the effective and group for the current session?
Answer: d) newgrp
19-How can you change the effective and group using the su command?
a) su -u new -g newgroup
b) su -u new
c) su -g newgroup
d) su new
Answer: a) su -u new -g newgroup
20-Which command is used to prevent login access by setting the ‘s shell to /usr/sbin/nologin?
Answer: a) nologin