Chmod Calculator
Frequently Asked Questions
What does chmod 755 mean?
chmod 755 gives the file owner full read, write, and execute permissions (rwx = 7), while group members and all other users get read and execute but not write (r-x = 5). This is the standard setting for web directories and executable scripts that anyone on the server may run.
What is the difference between chmod 644 and 755?
chmod 644 (rw-r--r--) is used for regular non-executable files such as HTML, CSS, and images — the owner can edit them and everyone else can read them. chmod 755 (rwxr-xr-x) adds execute permission for all users, making it appropriate for scripts, binaries, and directories that users need to enter with cd.
Is chmod 777 dangerous?
Yes. chmod 777 grants every user on the system full read, write, and execute access. On a shared or internet-facing server this is a critical security risk — any user or compromised process can modify or delete the file. Use 755 for directories and 644 for files in nearly all production scenarios.
How do I apply chmod recursively to a directory?
Add the -R flag: chmod -R 755 /path/to/directory. A safer pattern that skips wrong execute bits on plain files is: find /path -type d -exec chmod 755 {} \; for directories and find /path -type f -exec chmod 644 {} \; for files, applying the correct mode to each type separately.
What are the special permission bits setuid, setgid, and sticky?
Setuid (4xxx) runs an executable with the file owner's privileges. Setgid (2xxx) on a directory makes new files inherit the directory's group. The sticky bit (1xxx) on a directory — like /tmp with 1777 — prevents users from deleting files they do not own, even when they have write access to the directory.
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