方法一

users：此命令打印当前登录到当前主机的用户的用户名，但不显示有关来源、登录时间或者任何其他相关详细信息的任何信息

# users
jack ruchi aman rahul ramandeep

方法二

last：此命令搜索文件 /var/log/wtmp（或者由 -f 标志指定的文件）并显示自该文件创建以来登录（和退出）的所有用户的列表。
可以给出用户和 tty 的名称，在这种情况下，last 将仅显示与参数匹配的条目。

# last -a
 jack   pts/3        Tue Oct 16 18:01 - 18:01  (00:00)     10.10.10.30
 root     pts/2        Tue Oct 16 17:51   still logged in    10.10.10.30
 root     pts/1        Tue Oct 16 14:29 - 18:03  (03:34)     10.10.10.30
 root     pts/3        Tue Oct 16 11:10 - 13:11  (02:00)     10.10.10.30
 root     pts/1        Mon Oct 15 20:30 - 13:21  (16:51)     10.10.10.30
 root     pts/3        Mon Oct 15 18:02 - 18:37  (00:34)     10.10.10.30
 root     pts/1        Mon Oct 15 15:23 - 18:34  (03:11)     10.10.10.30
 root     pts/1        Mon Oct 15 10:45 - 15:22  (04:36)     10.10.10.30
 root     pts/2        Fri Oct 12 18:34 - 15:53 (3+21:19)    :2.0
 root     pts/1        Fri Oct 12 18:07 - 19:34  (01:27)     10.10.10.30
 root     pts/0        Fri Oct 12 17:57   still logged in    :0.0
root     tty1         Fri Oct 12 17:56   still logged in    :0
 reboot   system boot  Fri Oct 12 17:44 - 18:03 (4+00:19)    2.6.32-220.el6.i686

方法三

安全文件secure：此文件包含为登录机器所做的所有尝试的日志以及身份验证报告

# less /var/log/secure
Oct 16 18:01:12 localhost unix_chkpwd[3503]: password check failed for user (jack)
Oct 16 18:01:14 localhost sshd[3501]: Failed password for jack from 10.10.10.30 port 2326 ssh2
Oct 16 18:01:21 localhost passwd: pam_unix(passwd:chauthtok): password changed for jack
Oct 16 18:01:21 localhost passwd: gkr-pam: couldn't update the 'login' keyring password: no old password was entered
Oct 16 18:01:24 localhost sshd[3501]: Accepted password for jack from 10.10.10.30 port 2326 ssh2
Oct 16 18:01:24 localhost sshd[3501]: pam_unix(sshd:session): session opened for user jack by (uid=0)
Oct 16 18:01:31 localhost sshd[3501]: pam_unix(sshd:session): session closed for user jack

方法四

Finger：如果没有指定参数，Finger将为当前登录系统的每个用户打印一个条目。

# finger
 Login     Name       Tty      Idle  Login Time   Office      Office Phone
 jack               pts/3          Oct 16 18:01 (10.10.10.30)
 root      root       tty1       4d  Oct 12 17:56 (:0)
 root      root       pts/0    6:51  Oct 12 17:57 (:0.0)
 root      root       pts/1    2:08  Oct 16 14:29 (10.10.10.30)
 root      root       pts/2          Oct 16 17:51 (10.10.10.30)

方法五

who：此命令显示当前登录的用户以及时间详细信息

# who -u
 root     tty1         2012-10-12 17:56  old         1960 (:0)
 root     pts/0        2012-10-12 17:57 06:51        2376 (:0.0)
 root     pts/1        2012-10-16 14:29 02:09        3094  (10.10.10.30)
 root     pts/2        2012-10-16 17:51   .          3454 (10.10.10.30)

方法六

whoami：打印当前有效用户ID关联的用户名

# whoami
 root