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Utility last searches through the file /var/log/wtmp (or the file designated by the -f flag) and displays a list of all users logged in (and out) since that file was created in reverse chronological order. Names of users and ttyís can be given, in which case last will show only those entries matching the arguments. Linux version of last also displays IP or DNS, but unless option -a is given DNS names of machines from which user connected are abbreviated.
Utility lastb does the same for bad logs. As such it has great security value. Unfortunately few people know about its existence and even fewer use it. Often you need manually create the file /var/log/btmp for this command to be operational. It is not created automatically. For example:
# lastb -a lastb: /var/log/btmp: No such file or directory Perhaps this file was removed by the operator to prevent logging lastb info. # touch /var/log/btmp lastb -a btmp begins Mon Jul 1 18:57:15 2013
Command accepts either the name of the user or name of tty as a parameter. Names of tty can be abbreviated, thus last 0 is the same as last tty0. Without parameter information about all users is printed.
So there are three main forms of last and lastb commands:
With parameter meaning a user: last root; lastb root
The pseudo user reboot logs in each time the system is rebooted. Thus last reboot will show a log of all reboots since the log file was created.
|The pseudo user reboot logs in each time the system is rebooted. Thus, the command last reboot will show a log of all reboots since the log file was created.|
Lastb is the same as last, except that by default it shows a log of the file /var/log/btmp, which contains all the bad login attempts.
last [-R] [-num] [ -n num ] [-adiox] [ -f file ] [ -t YYYYMMDDHHMMSS ] [name...] [tty...]
lastb [-R] [-num] [ -n num ] [ -f file ] [-adiox] [name...] [tty...]
The files wtmp and btmp might not be found. The system only logs information in these files if they are present. This is a local configuration issue. If you want the command last and lastb to be operational both files should be created with a simple touch(1) command (for example, touch /var/log/wtmp). Most distributions create /var/log/wtmp) during the installation, but not /var/log/btmp.
- When last catches a SIGINT signal (generated by the interrupt key, usually Ctrl-C) or a SIGQUIT signal (generated by the quit key, usually Ctrl-\), last will show how far it has searched through the file; in the case of the SIGINT signal last will then terminate.
From the point of view of processing output in scripts, we can distinguish three output formats for last:
With the user name, including pseudo user reboot: last reboot (show only reboot)
The most important is output format last -a in which you can see full DNS name of client which logged to the server:
# last -a user1 pts/3 Mon Jul 1 08:35 still logged in joe.doer.vpn.firma.com user1 pts/3 Fri Jun 28 17:20 - 18:24 (01:03) lap245.firma.net root pts/2 Fri Jun 28 02:31 - 02:31 (00:00) user1 pts/2 Tue Jun 25 14:18 - 16:17 (01:58) lap245.firma.net root pts/3 Wed Jun 12 14:08 - 14:21 (00:13) root pts/3 Wed Jun 12 14:06 - 14:08 (00:01) root pts/3 Wed Jun 12 14:04 - 14:06 (00:02) user1 pts/2 Wed Jun 12 12:59 - 14:22 (01:22) joe.doer.vpn.firma.com user1 pts/2 Wed Jun 12 12:49 - 12:59 (00:10) joe.doer.vpn.firma.com oracle pts/1 Wed Jun 12 09:02 - 17:45 (08:43) 10.20.23.23 root pts/1 Wed Jun 5 17:54 - 17:56 (00:02) nti147.usfp2.basf.net root pts/2 Thu May 30 14:57 - 15:20 (00:23) nti106.firma.com oracle pts/1 Thu May 30 10:37 - 17:10 (06:33) lap719.firma.net user1 pts/2 Wed May 29 16:58 - 19:10 (02:12) joe.doer.vpn.firma.com
user2 pts/1 Fri Oct 14 10:17 - 10:17 (00:00) lap316.firma.com user2 pts/1 Fri Oct 14 10:17 - 10:17 (00:00) lap316.firma.com root ssh:notty Thu Oct 13 12:08 - 12:08 (00:00) srv016.firma.com root ssh:notty Thu Oct 13 12:08 - 12:08 (00:00) srv016.firma.com root ssh:notty Tue Sep 20 16:35 - 16:35 (00:00) lap316.firma.com root ssh:notty Wed Aug 10 17:05 - 17:05 (00:00) lap921.firma.com root ssh:notty Fri Jul 15 09:51 - 09:51 (00:00) lap921.firma.com root ssh:notty Fri Jul 15 09:51 - 09:51 (00:00) lap921.firma.com root ssh:notty Thu Jun 30 17:09 - 17:09 (00:00) lusytp02.firma.com roacle** pts/3 Thu Jun 30 16:58 - 16:58 (00:00) lapl61.firma.com root ssh:notty Thu Jun 30 12:24 - 12:24 (00:00) srv029.firma.com root ssh:notty Thu Jun 30 12:24 - 12:24 (00:00) srv029.firma.com user1 ssh:notty Tue Jun 28 14:22 - 14:22 (00:00) lap921.firma.com
With parameter meaning a user: last root; lastb root
, login(1), init(8)
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