Use `chmod` to change file permissions
Add execute permission: `chmod +x filename`
Remove execute permission: `chmod -x filename`
Set read, write, and execute for owner: `chmod u+rwx filename`
Set read and write for group: `chmod g+rw filename`
Set read permission for others: `chmod o+r filename`
Use numeric mode to set permissions: `chmod 755 filename`
Use numeric mode to set read and write for owner, read for group and others: `chmod 644 filename`
Change permissions recursively for a directory: `chmod -R 755 directory`
Check current permissions with `ls -l filename`
Change file owner with `chown user filename`
Change group with `chgrp group filename`
Change owner and group together: `chown user:group filename`