Setting Permissions Without Specifying u, g, o, or a

Permissions are set for user, group, and other if u, g, o, or a are not specified, but your umask (user file-creation mask) comes into play which makes things complicated. The most common umask is 022 which means that when you create a new directory the permissions are not the default of 777 ( drwxrwxrwx) but rather 777 – 022 which is 755 ( drwxr-xr-x). And when you create a new file, the permissions are not the default 666 ( -rw-rw-rw-) but rather 666 – 022 which is 644 ( -rw-r–r–).

The following will happen if your umask is the most common umask of 022:

Command (equivalent command using number system) Permissions
chmod =rwx myfile.txt chmod 755 myfile.txt -rwxr-xr-x

chmod +x myapp.bin