Top 10 Linux System Monitoring Tools Every Linux Geek Should Know

Are you in need of monitoring a Linux server for performance? These built-in command and add-on tools provide techniques which can be used to get useful information about a system’s activities. These tools will help find the possible causes of a performance problem. The commands I talk about below are some of the most basic commands when it comes to system analysis and debugging server issues.

top

Process Activity Command
The top program provides a awesome real-time view of your system for example actual process activity. Out the box, it displays the most CPU-intensive processes running on the Linux Machine and updates the list every five seconds.

vmstat

System Activity, Hardware and System Information

procs ———–memory———- —swap– —–io—- –system– —–cpu——
r b swpd free buff cache si so bi bo in cs us sy id wa st
0 0 0 2540988 522188 5130400 0 0 2 32 4 2 4 1 96 0 0
1 0 0 2540988 522188 5130400 0 0 0 720 1199 665 1 0 99 0 0
0 0 0 2540956 522188 5130400 0 0 0 0 1151 1569 4 1 95 0 0
0 0 0 2540956 522188 5130500 0 0 0 6 1117 439 1 0 99 0 0
0 0 0 2540940 522188 5130512 0 0 0 536 1189 932 1 0 98 0 0
0 0 0 2538444 522188 5130588 0 0 0 0 1187 1417 4 1 96 0 0
0 0 0 2490060 522188 5130640 0 0 0 18 1253 1123 5 1 94 0 0

w

Find Out Who Is Logged on And What They Are Doing

# w username
# w username

Sample output

17:58:47 up 5 days, 20:28, 2 users, load average: 0.36, 0.26, 0.24
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
root pts/0 10.1.3.145 14:55 5.00s 0.04s 0.02s vim /etc/resolv.conf
root pts/1 10.1.3.145 17:43 0.00s 0.03s 0.00s w

uptime

How Long The System Has Been Up

# uptime

output:

14:28:17 up 2 days, 3:53, 1 user, load average: 0.90, 0.46, 0.37

ps

Displays The Processes

# ps -A

Output:

PID TTY TIME CMD
1 ? 00:00:02 init
2 ? 00:00:02 migration/0
3 ? 00:00:01 ksoftirqd/0
4 ? 00:00:00 watchdog/0
5 ? 00:00:00 migration/1
6 ? 00:00:15 ksoftirqd/1
….
…..
4881 ? 00:53:28 java
4885 tty1 00:00:00 mingetty
4886 tty2 00:00:00 mingetty
4887 tty3 00:00:00 mingetty
4888 tty4 00:00:00 mingetty
4891 tty5 00:00:00 mingetty
4892 tty6 00:00:00 mingetty
4893 ttyS1 00:00:00 agetty
12853 ? 00:00:00 cifsoplockd
12854 ? 00:00:00 cifsdnotifyd
14231 ? 00:10:34 lighttpd
14232 ? 00:00:00 php-cgi
54981 pts/0 00:00:00 vim
55465 ? 00:00:00 php-cgi
55546 ? 00:00:00 bind9-snmp-stat
55704 pts/1 00:00:00 ps

free

Memory Usage

# free

Output:

total used free shared buffers cached
Mem: 1024768 316332 708436 0 34536 123616
-/+ buffers/cache: 158180 866588
Swap: 463868 176 463692

iostat

Average CPU Load, Disk Activity
The command iostat report Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions and network filesystems (NFS).

The command iostat report Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions and network filesystems (NFS).

output:

Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in) 06/26/2009
avg-cpu: %user %nice %system %iowait %steal %idle
3.50 0.09 0.51 0.03 0.00 95.86
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 22.04 31.88 512.03 16193351 260102868
sda1 0.00 0.00 0.00 2166 180
sda2 22.04 31.87 512.03 16189010 260102688
sda3 0.00 0.00 0.00 1615 0

ss

Network Statistics
ss command is used to dump socket statistics.

FIN-WAIT-2 0 0 10.1.10.72:www 131.142.24.171:51858
ESTAB 0 0 10.1.10.72:ssh 10.1.10.157:35827
ESTAB 0 0 10.1.10.72:ssh 10.1.10.157:59810
ESTAB 0 0 10.1.10.72:www 131.142.24.171:51857
ESTAB 0 0 10.1.10.72:www 8.22.204.204:2336
FIN-WAIT-2 0 0 10.1.10.72:www 131.142.24.171:51860

iptraf

Real-time Network Statistics

tcpdump

Detailed Network Traffic Analysis
tcpdump is a simple command that dumps traffic on a network. You might need good understanding of TCP/IP protocol to use this tool. For example to display traffic info about DNS, enter:

# tcpdump -i eth1 ‘udp port 53′

To display all HTTP session to 10.1.10.12:

# tcpdump -ni eth0 ‘dst 10.1.10.12 and tcp and port http’