The 755 permission setting in Linux grants the owner full read, write, and execute rights while giving others only read and execute access. If you have ever wondered what is 755 permission in linux, this guide will break it down simply. You will learn how it works, when to use it, and how to apply it.
Permissions in Linux can feel confusing at first. But once you understand the basics, they become easy to manage. The 755 permission is one of the most common settings you will encounter. It is used for scripts, directories, and executable files.
What Is 755 Permission In Linux
This permission setting is a numeric representation of file access rights. In Linux, every file and directory has three sets of permissions: one for the owner, one for the group, and one for others. The number 755 breaks down into three digits: 7, 5, and 5.
The first digit (7) gives the owner full control. The second digit (5) gives the group read and execute access. The third digit (5) gives everyone else read and execute access. No one except the owner can write to the file or directory.
Breaking Down The Numeric Values
Each permission has a numeric value: read is 4, write is 2, and execute is 1. You add these numbers together to get the final digit. For example, 7 equals read (4) plus write (2) plus execute (1). The number 5 equals read (4) plus execute (1).
- 4 = read (r)
- 2 = write (w)
- 1 = execute (x)
- 7 = rwx (full access)
- 5 = r-x (read and execute only)
- 0 = — (no access)
So 755 means the owner can read, write, and execute. The group and others can only read and execute. This is a secure default for many system files and scripts.
When To Use 755 Permissions
You will use 755 for directories that need to be browsed by others. For example, a web server’s public folder often uses 755. This allows visitors to view files but not modify them.
Executable scripts also commonly use 755. If you write a bash script and want others to run it, set it to 755. The owner can edit it, but others can only execute it.
Never use 755 for sensitive files like password databases or private keys. Those should use stricter permissions like 600 or 700.
How To Set 755 Permissions
Setting permissions in Linux is straightforward. You use the chmod command. The syntax is simple: chmod 755 filename. Replace “filename” with the actual file or directory name.
Setting Permissions On A File
Open your terminal. Navigate to the directory containing the file. Then run the command:
chmod 755 myscript.shThis changes the permissions of myscript.sh to 755. You can verify it with ls -l. The output will show -rwxr-xr-x for the file.
Setting Permissions On A Directory
Directories work the same way. Use chmod 755 myfolder. The execute permission on a directory allows users to enter it. Without execute, they cannot list or access files inside.
chmod 755 /var/www/htmlThis gives the web server access to serve files from that directory. Users can browse it but not upload or modify files.
Recursive Permission Changes
Sometimes you need to change permissions for an entire folder tree. Use the -R flag for recursive changes. Be careful, as this can affect many files at once.
chmod -R 755 /path/to/directoryThis sets all files and subdirectories inside that path to 755. It is usefull for web server directories or shared project folders.
Understanding The Symbolic Representation
The symbolic form of 755 is rwxr-xr-x. The first three characters are for the owner: rwx. The next three are for the group: r-x. The last three are for others: r-x.
Each character has a meaning:
- r = read permission
- w = write permission
- x = execute permission
- – = no permission
When you see -rwxr-xr-x, the first dash indicates it is a file. For directories, you will see a “d” instead, like drwxr-xr-x.
Comparing 755 With Other Common Permissions
You will often see 644, 700, and 777. Each serves a different purpose. Here is a quick comparison:
- 644: Owner can read and write; others can only read. Good for regular files.
- 700: Owner has full access; others have none. Best for private scripts.
- 755: Owner has full access; others can read and execute. Standard for executables.
- 777: Everyone has full access. Avoid this for security reasons.
Using 777 is risky because anyone can modify the file. Stick with 755 for most shared executable files.
Common Use Cases For 755
Web servers often require 755 for directories. For example, Apache or Nginx need to read files in the public directory. The server runs as a specific user, and 755 ensures it can access the files.
System binaries in /usr/bin or /usr/local/bin usually have 755. This allows all users to run them but only root to modify them.
Shared scripts in a development team also benefit from 755. Everyone can run the script, but only the owner can edit it. This prevents accidental changes.
Security Implications Of 755
While 755 is safe for most cases, it is not perfect. The group and others can read the file. If the file contains sensitive logic or credentials, use 700 instead.
For directories, 755 allows anyone to list its contents. If you have a directory with private files, set it to 700 or 750.
Always consider who needs access. If only one user should modify the file, use 755 only if others need to execute it. Otherwise, use 700.
How To Check Current Permissions
Use the ls -l command to see permissions. The output shows the permission string, number of links, owner, group, size, date, and filename.
ls -l myscript.shExample output:
-rwxr-xr-x 1 user group 1234 Jan 1 12:00 myscript.shThe first part -rwxr-xr-x tells you it is a file with 755 permissions. The owner is “user” and the group is “group”.
Using Stat Command
The stat command gives more details. It shows the numeric permissions in octal form.
stat -c "%a %n" myscript.shThis outputs something like “755 myscript.sh”. It is a quick way to confirm the numeric value.
Changing Ownership Along With Permissions
Permissions work with ownership. The owner and group must be correct for 755 to be effective. Use chown to change ownership.
chown user:group myscript.shAfter setting the correct owner, apply 755 permissions. This ensures only the intended user can write to the file.
Common Mistakes With 755
One mistake is applying 755 to sensitive files. For example, SSH private keys should have 600 permissions. Using 755 on them exposes your keys to anyone on the system.
Another mistake is forgetting the -R flag for directories. If you set 755 on a directory without recursion, subdirectories may retain insecure permissions.
Also, do not use 755 on files that should not be executable. Regular text files or configuration files should use 644. Unnecessary execute permissions can be a security risk.
Practical Examples
Let us walk through a real scenario. You have a web application in /var/www/myapp. You want the web server to read files but not write to them.
- Set the directory to 755:
chmod 755 /var/www/myapp - Set files inside to 644:
chmod 644 /var/www/myapp/* - Make sure the owner is the web server user:
chown -R www-data:www-data /var/www/myapp
This setup is secure. The web server can serve files, but no one can modify them through the web.
Another Example: A Shared Script
Your team has a backup script in /usr/local/bin/backup.sh. You want everyone to run it but only you to edit it.
- Set ownership:
chown youruser:yourgroup /usr/local/bin/backup.sh - Set permissions:
chmod 755 /usr/local/bin/backup.sh - Verify:
ls -l /usr/local/bin/backup.sh
Now all users can execute the backup script. Only you can modify it.
Understanding The Octal System
The numbers 0-7 come from octal representation. Each digit corresponds to a set of three binary bits. For example, 7 in binary is 111, meaning all three permissions are set. The number 5 is 101, meaning read and execute but not write.
This system is efficient. You can represent all combinations with a single digit. It is widely used in Unix-like systems.
Why 755 Is The Default For Many Files
When you create a new file, the system applies a default umask. The umask subtracts permissions from the base value. For example, a base of 666 minus a umask of 022 gives 644. For directories, base 777 minus 022 gives 755.
This is why many directories default to 755. It balances access and security. You can change the umask to alter defaults.
Troubleshooting Permission Issues
If a script fails to run, check permissions first. Use ls -l to see if the execute bit is set. If it shows -rw-r--r--, you need to add execute permission.
Another common issue is directory permissions. If you cannot access a directory, check if it has execute permission for your user. Without it, you cannot enter the directory.
Use chmod u+x filename to add execute for the owner. Or use chmod 755 filename to set it fully.
When 755 Is Not Enough
Sometimes you need more granular control. For example, you might want the group to have write access but not others. In that case, use 775 instead of 755.
For sensitive files, use 700. For shared editing, use 775. Always choose the least permissive setting that still works.
Frequently Asked Questions
What does 755 permission mean in Linux?
It means the owner can read, write, and execute. The group and others can only read and execute. It is written as rwxr-xr-x.
How do I change file permissions to 755?
Use the command chmod 755 filename in the terminal. Replace “filename” with your file’s name.
Is 755 permission safe for web directories?
Yes, it is standard for web server directories. It allows the server to read files but not write to them. Avoid using 777.
What is the difference between 755 and 777?
755 gives write access only to the owner. 777 gives write access to everyone. 777 is less secure and should be avoided.
Can I use 755 on a directory?
Yes, it is common for directories. It allows users to list and enter the directory but not modify files unless they own them.
Final Thoughts On 755 Permissions
Understanding what is 755 permission in linux is essential for managing files and directories. It provides a good balance between access and security. Use it for executable scripts and shared directories.
Always check your permissions with ls -l. Avoid using 777 unless absolutely necessary. With practice, you will find 755 to be a reliable default for many situations.
Remember to set ownership correctly with chown. Permissions alone do not secure a file if the wrong user owns it. Combine both for best results.
Now you can confidently apply 755 permissions to your Linux files. It is a simple yet powerful tool in your system administration kit.