File permissions

Linux permissions control read (r), write (w) and execute (x) access for the file owner, group and everyone else.

ls -l file.txtchmod u+x script.shchmod g-w file.txtchmod o-r file.txtchmod 644 file.txtchmod 755 script.shchmod -R 750 directory/chown user file.txtchown user:group file.txtchown -R user:group directory/chgrp group file.txt

chmod changes permission bits. Symbolic notation uses u for owner, g for group and o for others, followed by +, - or = and the permission.

Numeric notation adds 4 for read, 2 for write and 1 for execute. 644 gives the owner read/write and everyone else read-only. 755 gives the owner read/write/execute and everyone else read/execute.

chown changes ownership and chgrp changes the group. -R applies changes recursively. Recursive permission changes can affect large directory trees, so check the target path carefully.

umask controls which permission bits are removed from defaults when new files and directories are created.