login
initiates a user session on the system
TLDR
Log in as user
$ login [user]
Log in without authentication$ login -f [user]
Log in preserving environment$ login -p [user]
Log in from remote host$ login -h [host] [user]
SYNOPSIS
login [options] [username]
DESCRIPTION
login initiates a user session on the system. It authenticates users, sets up the environment, and starts a shell. This command is typically invoked by init or a terminal program.
PARAMETERS
-f
Skip authentication (for preauthenticated users)-p
Preserve environment variables-h HOST
Specify remote hostname (for remote logins)
CAVEATS
Direct invocation is restricted to root or when called from specific programs. The -f option is only available to root. PAM modules control authentication behavior.
HISTORY
The login command dates back to the original Unix systems at Bell Labs in the 1970s, providing the fundamental user authentication mechanism.