當你新登錄一個主機，過着管理一個主機，這時候你就需要這些命令來進行查看了：
1. w : Show who is logged on and what they are doing.
w [options] user [...]
常用命令：
w -h --no-header
w -u --no-current
w -s : Use the short format. Don't print the login time, JCPU or PCPU times.
w -i, --ip-addr : Display IP address instead of hostname for from field.
2. who : Show who is logged on
who -a, --all 展示所有的; 相當於 使用 -b -d --login -p -r -t -T -u
3. users: Print the user names of users currently logged in to the current host
4. whoami : Print effective userid
Print the user name associated with the current effective user ID. Same as id -un.
5. last : last, lastb - show a listing of last logged in users
last -a
last [options] [username...] [tty...]
last searches back through the /var/log/wtmp file (or the file designated by the -f option) and displays a list of all users logged in
(and out) since that file was created. One or more usernames and/or ttys can be given, in which case last will show only the entries
matching those arguments. Names of ttys can be abbreviated, thus last 0 is the same as last tty0.
When catching a SIGINT signal (generated by the interrupt key, usually control-C) or a SIGQUIT signal, last will show how far it has
searched through the file; in the case of the SIGINT signal last will then terminate.
The pseudo user reboot logs in each time the system is rebooted. Thus last reboot will show a log of all the reboots since the log file
was created.
lastb is the same as last, except that by default it shows a log of the /var/log/btmp file, which contains all the bad login attempts.
last reboot 展示所有的機器重新啟動的情況。
6. lastb：lastb is the same as last, except that by default it shows a log of the /var/log/btmp file, which contains all the bad login attempts.
在root 權限下，使用 lastb 命令，將會顯示所有嘗試登錄失敗的情況。
保持更新，轉載請注明出處。