Master Linux System Monitoring: date, uptime, w, top, who, and last Commands

date

The date command is the classic way to display the current system time and is frequently used in scripts to define timestamps.

uptime

[root@localhost ~]# uptime
16:51:24 up 13:02,  1 user,  load average: 0.00, 0.01, 0.05

The first value shows the current time, the second indicates how long the system has been running, the third shows the number of logged‑in users, and the three numbers at the end are the average load over the past 1, 5, and 15 minutes.

w

[modps@gd-mopps02 ~]$ w 17:19:01 up 1983 days, 13:05, 2 users, load average: 26.45, 27.76, 27.72 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT gdmm81 pts/0 10.153.97.38 14:09 23.00s 0.36s 0.01s sshd: gdmm81 [priv] dwtangmi pts/3 10.153.97.56 17:18 0.00s 0.07s 0.01s sshd: dwtangmingqi [priv]

The w command shows who is currently logged in, what they are doing, and how their activity affects system load. It combines the information of uptime, who, and ps -a. Key columns are:

User : login name

TTY : terminal identifier assigned after login

From : remote host name or IP

login@ : login time

IDLE : idle time (reset on any user activity)

JCPU : total CPU time for all processes attached to the terminal, including background jobs

PCPU : CPU time for the current process

WHAT : command line of the running process

top

The top command provides a real‑time view of running processes, refreshing every three seconds by default. It also supports various options to customize the display.

who

[modps@gd-mopps02 ~]$ who
gdmm81   pts/0        2019-01-18 14:09 (10.153.97.38)
dwtangmingqi pts/3   2019-01-18 17:18 (10.153.97.56)

The who command is similar to w but provides slightly less detail, listing each logged‑in user along with their terminal, login time, and originating host.

last

[root@localhost ~]# last root -F | head -1 | awk '{print $4,$5,$6,$7,$8}'
Fri Jan 18 14:55:52 2019

The last command lists recent login sessions. The example extracts the most recent login time for the user root. The -F flag adds full login and logout timestamps, which can be explored further.