Which command is used to set file permissions in Linux?

The command used to set file permissions in Linux is chmod. This command allows users to modify the read, write, and execute permissions associated with files and directories. Each file and directory has three sets of permissions: one for the owner, one for the group, and one for others. With chmod, you can specify permissions explicitly in numeric form (like 755) or using symbolic representations (like u+x, which adds execute permissions for the user).

For example, if you want to allow the owner to read, write, and execute a file, while allowing the group to read and others to have no permissions, you would use the command chmod 740 filename. This flexibility in setting permissions is crucial for maintaining proper access control and security on a Linux system.

In contrast, the other options serve different purposes. The command setfacl is used to set access control lists, allowing more granular permissions beyond the traditional user/group/other model. The chown command changes the ownership of a file or directory, effectively altering who the owner is rather than the permissions themselves. Finally, umask is utilized to set the default file permissions for newly created files and directories, influencing the permissions assigned when these files are created