In UNIX and Linux, the "who" utility displays a list of all users currently logged on to a specific terminal and at what time they logged on. The "who" utility may also display the remote host name if the particular user is not logged in from a local terminal.
Sometimes, the number of users on a terminal can be so large that it becomes difficult to find a single user. In such cases, the "grep" command is used in conjunction with the utility, and the user name, if known, is supplied in the command line. This is denoted as, for example, "who | grep smij." This command returns just one line that lists user "smij" and at what time he logged on.