Linux File Permissions and Management Guide
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:
Contents
ls – List Files
- The ls command is used to list the files and directories in a directory. It also displays file permissions.
ls -l
Example output:
-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 – Change File Permissions
- The chmod command is used to change file permissions.
- You can modify permissions using symbolic or octal notation.
- To add read and write permissions for the owner of a file:
chmod u+rw myfile.txt
- To remove write permissions for others:
chmod o-w myfile.txt
- To set permissions using octal notation (e.g., read, write, and execute for the owner, and read-only for others):
chmod 744 myfile.txt
chown – Change File Ownership
- The chown command is used to change the owner and group of a file or directory.
- Change the owner of a file to a different :
chown new myfile.txt
- Change the group of a file to a different group:
chown :newgroup myfile.txt
chgrp – Change Group Ownership
- The chgrp command is used to change the group ownership of a file or directory.
chgrp newgroup myfile.txt
umask – Set Default Permissions
- The umask command is used to set the default permissions for newly created files and directories.
To set a default umask for a to allow read and write for themselves and read-only for others:
umask 022
ls – List Files
List files and directories, displaying file permissions, ownership, and other details.
Example:
ls -l
chmod – Change File Permissions
Modify file permissions using symbolic or octal notation.
Example (add read and write permissions for the owner):
chmod u+rw myfile.txt
chown – Change File Ownership
Change the owner and/or group of a file or directory.
Example (change the owner of a file):
chown new myfile.txt
chgrp – Change Group Ownership
Change the group ownership of a file or directory.
Example (change the group of a file):
chgrp newgroup myfile.txt
umask – Set Default Permissions
Set default permissions for newly created files and directories.
Example (set a default umask):
umask 022
passwd – Change Password
Change a ‘s password.
Example:
passwd name
su – Switch
Switch to another account with super privileges.
Example (switch to the root ):
su
sudo – Execute a Command with Super Privileges
Run a command with super (root) privileges.
Example (update system packages with sudo):
sudo apt update
chown – Change Ownership Recursively
Change ownership recursively for a directory and its contents.
Example (change owner and group recursively):
chown -R new:newgroup mydirectory/
find – Search for Files and Directories
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
- These commands are fundamental for managing file permissions, ownership, and access control on a Linux system.
- Always use these commands with caution, especially when working with system-critical files and directories to avoid unintended consequences.
umask – Display Current umask
Display the current umask value, which controls default permissions for new files and directories.
Example:
umask
id – Display and Group Information
Display the and group information for the current .
Example:
id
groups – List Groups
List the groups to which the current belongs.
Example:
groups
setfacl – Set File Access Control Lists
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
getfacl – Get File Access Control Lists
Display the access control lists (ACLs) for a file or directory.
Example:
getfacl myfile.txt
setgid – Set Group ID on Execution
Set the set group ID (SGID) on a directory to ensure new files inherit the group ownership of the directory.
Example:
chmod g+s mydirectory/
sticky – Set the Sticky Bit
Set the sticky bit on a directory to restrict file deletion to the file owner.
chmod +t mydirectory/
passwd – Change Group Password
Change the password for a group.
Example:
sudo passwd groupname
add – Add a New
Create a new account on the system.
Example:
sudo add new
del – Delete a
Delete a account and associated files from the system.
Example:
sudo del old
mod – Modify Account
Modify account properties, including group membership and ID.
Example (add to a group):
sudo mod -aG newgroup new
chattr – Change File Attributes
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:
getent – Get Entries from Administrative Databases
Retrieve entries from various administrative databases, including and group information.
Example (get information):
getent passwd name
passwd – Set Password Expiration and Aging Information
Set password expiration and aging information for a account.
Example (set password expiration date for a ):
chage -E 2024-12-31 name
sudoers – Edit the sudoers File
Edit the sudoers file to configure sudo access and permissions for s and groups.
Example (edit the sudoers file):
sudo visudo
newgrp – Change the Effective Group ID
Change the effective group ID for the current session.
Example:
newgrp newgroup
groups – Display ‘s Groups
Display the group memberships for a specific .
Example:
groups name
setuid – Set ID on Execution
Set the set ID (SUID) on an executable file to run with the owner’s privileges.
Example:
chmod u+s myprogram
passwd -l – Lock Account
Lock a account to prevent login access.
Example:
sudo passwd -l name
passwd -u – Unlock Account
Unlock a previously locked account.
Example:
sudo passwd -u name
nologin – Prevent Login
Set the ‘s shell to /usr/sbin/nologin to prevent login access.
Example:
sudo mod --shell /usr/sbin/nologin name
su – Change and Group
Change the effective and group by specifying them with the -u and -g options.
Example:
su -u new -g newgroup
who – Display Information About Logged-In s
Show information about s who are currently logged in.
Example:
who
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.
Quiz with answers
Here’s a quiz about the Linux commands related to file permissions and management, along with the answers:
Quiz: Linux File Permissions and Management
1-What command is used to list files and directories with their permissions, ownership, and other details?
a) cat
b) ls
c) dir
d) fileinfo
Answer: b) ls
2-Which command is used to change file permissions?
a) modfile
b) chown
c) chmod
d) setperm
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?
a) changeown
b) chown
c) change
d) ownerchange
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 .
d) Switch
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?
a) aclset
b) getfacl
c) setfacl
d) accessctl
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?
a) sudoedit
b) visudo
c) sudoconfig
d) editsudo
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?
a) whoami
b) logininfo
c) who
d) list
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?
a) setgid
b) sgid
c) chmod g+s
d) sgidset
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?
a) getent
b) lookup
c) admindb
d) getdb
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?
a) groups
b) showgroups
c) listgroups
d) groupinfo
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?
a) switch
b) chgusrgrp
c) set
d) newgrp
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?
a) nologin
b) nologin
c) noaccess
d) denylogin
Answer: a) nologin