One of our regular reader asks:
I’d like to discover information about who is currently using the system. When a user logs in what files are updated in UNIX / Linux?
Linux / UNIX have utmp and wtmp files to keep login records. Following three files keeps track of all logins and logouts to the system.
=> /var/run/utmp : List of current login sessions.
=> /var/log/wtmp : Database of past user logins / previous login sessions.
=> /var/log/lastlog : Last logins information about users
How do I access login records files?
These are a binary log files, and grows linearly at its end. So you cannot view records using cat or other text based utilities. The file <utmp.h> declares the structures used to record information about current users in the file. This can be accessed using C programs or other specialized utilities:
- The utmp file is used and accessed by the following commands:
- The wtmp file is used and accessed by the following command:
- Man pages – ac(1), date(1), last(1), login(1), who(1), getutent(3), updwtmp(3), init(8), wtmp(5)
- Header file /usr/include/utmp.h