Learn / CHMOD simulator

CHMOD simulator

Every file on Linux says who may read it, write it and execute it: its owner, its group, and everyone else. Click the permissions, or type a number, and see what it means.

OWNER

GROUP

OTHERS

OR TYPE A NUMBER

COMMON VALUES

644

-rw-r--r--

COMMAND

chmod 644 file.txt

How the number works. Read is 4, write is 2, execute is 1: add them up for each of the three groups. 7 = 4+2+1 = everything, 6 = read and write, 5 = read and execute, 0 = nothing. The letters show the same thing: r read, w write, x execute, - not allowed. You see them with ls -l.

On folders the meaning changes a little: read lets you list the names inside, write lets you create and delete files in it, and execute lets you enter it. A folder almost always needs x together with r.

Avoid 777. It lets every user and every program on the PC change the file. If something only works with 777, the real problem is usually the owner of the file: check it with ls -l and fix it with sudo chown. SSH keys must be private: chmod 600 ~/.ssh/id_ed25519.

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