What does chmod 755 mean?
Breaking down the numbers
The three digits in 755 represent permissions for the owner, group, and others, in that order. Each digit is a sum: read (4), write (2), and execute (1). So 7 = 4+2+1 (read, write, execute), and 5 = 4+1 (read and execute).
For a file, execute permission means you can run it as a program or script. For a directory, execute permission means you can enter it and access files inside. Without execute on a directory, you can't cd into it or list its contents even if you have read permission.
When to use 755
Use 755 for directories and for executable files that should be readable by everyone but only writable by the owner. It's common for web server document roots and system binaries.
Avoid 755 for sensitive files like private keys or config files containing passwords. Those should be 600 (owner read/write only) or 640 (owner read/write, group read).
- 755 = rwxr-xr-x
- 700 = rwx------ (owner only)
- 644 = rw-r--r-- (regular files, no execute)
- 600 = rw------- (private files)
- 777 = rwxrwxrwx (everyone can write — avoid)
How to apply it
Run chmod 755 filename to set permissions on a single file or directory. To apply recursively to a directory tree, use chmod -R 755 directoryname, but be careful: that makes every file executable, which is rarely what you want.
You can also use symbolic mode: chmod u=rwx,go=rx filename does the same thing and can be easier to read.
Common mistakes
- Thinking 755 gives everyone full access — it doesn't; group and others cannot write.
- Using 777 as a quick fix for permission errors, which lets any user modify the file and is a security risk.
- Applying chmod -R 755 to a whole web directory, which makes all files executable when they shouldn't be.
