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:
Suggested readings:
- 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
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| Category | List of Unix and Linux commands |
|---|---|
| File Management | cat |
| Firewall | Alpine Awall • CentOS 8 • OpenSUSE • RHEL 8 • Ubuntu 16.04 • Ubuntu 18.04 • Ubuntu 20.04 |
| Network Utilities | dig • host • ip • nmap |
| OpenVPN | CentOS 7 • CentOS 8 • Debian 10 • Debian 8/9 • Ubuntu 18.04 • Ubuntu 20.04 |
| Package Manager | apk • apt |
| Processes Management | bg • chroot • cron • disown • fg • jobs • killall • kill • pidof • pstree • pwdx • time |
| Searching | grep • whereis • which |
| User Information | groups • id • lastcomm • last • lid/libuser-lid • logname • members • users • whoami • who • w |
| WireGuard VPN | Alpine • CentOS 8 • Debian 10 • Firewall • Ubuntu 20.04 |
Nikhil,
Oh I just forgot about lastb., I appreciate your post.
Can you pls tell me how to information on this log files
there is apparently another file which not many know of is /var/log/btmp and the related command to read it is lastb.
lastb is same as that of last except that it shows all the bad login attempts which are recorded into /var/log/btmp, if the file is not present you would have to touch it to get started.
Nikhil
lsof will give you a list of all files being accessed at the moment and the users that are accessing them, among other things.