Need to monitor Linux server performance? Try these built-in commands and a few add-on tools. Most distributions come with tons of Linux monitoring tools. These tools provide metrics which can be used to get information about system activities. You can use these tools to find the possible causes of a performance problem. The commands discussed below are some of the most fundamental commands when it comes to system analysis and debugging Linux server issues such as:
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1.Finding out system bottlenecks
2.Disk (storage) bottlenecks
3.CPU and memory bottlenecks
4.Network bottleneck.
1. top – Process activity monitoring command
top command display Linux processes. It provides a dynamic real-time view of a running system i.e. actual process activity. By default, it displays the most CPU-intensive tasks running on the server and updates the list every five seconds.
top - Linux monitoring commandCommonly Used Hot Keys With top Linux monitoring tools
Here is a list of useful hot keys:
Hot Key | Usage |
t | Displays summary information off and on. |
m | Displays memory information off and on. |
A | Sorts the display by top consumers of various system resources. Useful for quick identification of performance-hungry tasks on a system. |
f | Enters an interactive configuration screen for top. Helpful for setting up top for a specific task. |
o | Enables you to interactively select the ordering within top. |
r | Issues renice command. |
k | Issues kill command. |
z | Turn on or off color/mono |
How do I Find Out Linux CPU Utilization?
2. vmstat – Virtual memory statistics
The vmstat command reports information about processes, memory, paging, block IO, traps, and cpu activity.
# vmstat 3
Sample Outputs:
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
Display Memory Utilization Slabinfo
# vmstat -m
Get Information About Active / Inactive Memory Pages
# vmstat -a
How do I find out Linux Resource utilization to detect system bottlenecks?
3. w – Find out who is logged on and what they are doing
w command displays information about the users currently on the machine, and their processes.
# w username
# w vivek
Sample Outputs:
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
4. uptime – Tell how long the Linux system has been running
uptime command can be used to see how long the server has been running. The current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.
# uptime
Output:
18:02:41 up 41 days, 23:42, 1 user, load average: 0.00, 0.00, 0.00
1 can be considered as optimal load value. The load can change from system to system. For a single CPU system 1 – 3 and SMP systems 6-10 load value might be acceptable.
5. ps – Displays the Linux processes
ps command will report a snapshot of the current processes. To select all processes use the -A or -e option:
# ps -A
Sample Outputs:
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
ps is just like top but provides more information.
Show Long Format Output
# ps -Al
To turn on extra full mode (it will show command line arguments passed to process):
# ps -AlF
Display Threads ( LWP and NLWP)
# ps -AlFH
Watch Threads After Processes
# ps -AlLm
Print All Process On The Server
# ps ax
# ps axu
Want To Print A Process Tree?
# ps -ejH
# ps axjf
# pstree
Get Security Information of Linux Process
# ps -eo euser,ruser,suser,fuser,f,comm,label
# ps axZ
# ps -eM
Let Us Print Every Process Running As User Vivek
# ps -U vivek -u vivek u
Configure ps Command Output In a User-Defined Format
# ps -eo pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:14,comm
# ps axo stat,euid,ruid,tty,tpgid,sess,pgrp,ppid,pid,pcpu,comm
# ps -eopid,tt,user,fname,tmout,f,wchan
Try To Display Only The Process IDs of Lighttpd
# ps -C lighttpd -o pid=
OR
# pgrep lighttpd
OR
# pgrep -u vivek php-cgi
Print The Name of PID 55977
# ps -p 55977 -o comm=
Top 10 Memory Consuming Process
# ps -auxf | sort -nr -k 4 | head -10
Show Us Top 10 CPU Consuming Process
# ps -auxf | sort -nr -k 3 | head -10
Show All Running Processes in Linux
6. free – Show Linux server memory usage
free command shows the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel.
# free
Sample Output:
total used free shared buffers cached
Mem: 12302896 9739664 2563232 0 523124 5154740
-/+ buffers/cache: 4061800 8241096
Swap: 1052248 0 1052248
7. iostat – Montor Linux average CPU load and disk activity
iostat command report Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions and network filesystems (NFS).
# iostat
Sample Outputs:
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
Linux Track NFS Directory / Disk I/O Stats
8. sar – Monitor, collect and report Linux system activity
sar command used to collect, report, and save system activity information. To see network counter, enter:
# sar -n DEV | more
The network counters from the 24th:
# sar -n DEV -f /var/log/sa/sa24 | more
You can also display real time usage using sar:
# sar 4 5
Sample Outputs:
Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in) 06/26/2009
06:45:12 PM CPU %user %nice %system %iowait %steal %idle
06:45:16 PM all 2.00 0.00 0.22 0.00 0.00 97.78
06:45:20 PM all 2.07 0.00 0.38 0.03 0.00 97.52
06:45:24 PM all 0.94 0.00 0.28 0.00 0.00 98.78
06:45:28 PM all 1.56 0.00 0.22 0.00 0.00 98.22
06:45:32 PM all 3.53 0.00 0.25 0.03 0.00 96.19
Average: all 2.02 0.00 0.27 0.01 0.00 97.70
9. mpstat – Monitor multiprocessor usage on Linux
mpstat command displays activities for each available processor, processor 0 being the first one. mpstat -P ALL to display average CPU utilization per processor:
# mpstat -P ALL
Sample Output:
Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in) 06/26/2009
06:48:11 PM CPU %user %nice %sys %iowait %irq %soft %steal %idle intr/s
06:48:11 PM all 3.50 0.09 0.34 0.03 0.01 0.17 0.00 95.86 1218.04
06:48:11 PM 0 3.44 0.08 0.31 0.02 0.00 0.12 0.00 96.04 1000.31
06:48:11 PM 1 3.10 0.08 0.32 0.09 0.02 0.11 0.00 96.28 34.93
06:48:11 PM 2 4.16 0.11 0.36 0.02 0.00 0.11 0.00 95.25 0.00
06:48:11 PM 3 3.77 0.11 0.38 0.03 0.01 0.24 0.00 95.46 44.80
06:48:11 PM 4 2.96 0.07 0.29 0.04 0.02 0.10 0.00 96.52 25.91
06:48:11 PM 5 3.26 0.08 0.28 0.03 0.01 0.10 0.00 96.23 14.98
06:48:11 PM 6 4.00 0.10 0.34 0.01 0.00 0.13 0.00 95.42 3.75
06:48:11 PM 7 3.30 0.11 0.39 0.03 0.01 0.46 0.00 95.69 76.89
Linux display each multiple SMP CPU processors utilization individually.
10. pmap – Montor process memory usage on Linux
pmap command report memory map of a process. Use this command to find out causes of memory bottlenecks.
# pmap -d PID
To display process memory information for pid # 47394, enter:
# pmap -d 47394
Sample Outputs:
47394: /usr/bin/php-cgi
Address Kbytes Mode Offset Device Mapping
0000000000400000 2584 r-x-- 0000000000000000 008:00002 php-cgi
0000000000886000 140 rw--- 0000000000286000 008:00002 php-cgi
00000000008a9000 52 rw--- 00000000008a9000 000:00000 [ anon ]
0000000000aa8000 76 rw--- 00000000002a8000 008:00002 php-cgi
000000000f678000 1980 rw--- 000000000f678000 000:00000 [ anon ]
000000314a600000 112 r-x-- 0000000000000000 008:00002 ld-2.5.so
000000314a81b000 4 r---- 000000000001b000 008:00002 ld-2.5.so
000000314a81c000 4 rw--- 000000000001c000 008:00002 ld-2.5.so
000000314aa00000 1328 r-x-- 0000000000000000 008:00002 libc-2.5.so
000000314ab4c000 2048 ----- 000000000014c000 008:00002 libc-2.5.so
.....
......
..
00002af8d48fd000 4 rw--- 0000000000006000 008:00002 xsl.so
00002af8d490c000 40 r-x-- 0000000000000000 008:00002 libnss_files-2.5.so
00002af8d4916000 2044 ----- 000000000000a000 008:00002 libnss_files-2.5.so
00002af8d4b15000 4 r---- 0000000000009000 008:00002 libnss_files-2.5.so
00002af8d4b16000 4 rw--- 000000000000a000 008:00002 libnss_files-2.5.so
00002af8d4b17000 768000 rw-s- 0000000000000000 000:00009 zero (deleted)
00007fffc95fe000 84 rw--- 00007ffffffea000 000:00000 [ stack ]
ffffffffff600000 8192 ----- 0000000000000000 000:00000 [ anon ]
mapped: 933712K writeable/private: 4304K shared: 768000K
The last line is very important:
•.mapped: 933712K total amount of memory mapped to files
•.writeable/private: 4304K the amount of private address space
•.shared: 768000K the amount of address space this process is sharing with others
Linux find the memory used by a program / process using pmap command
11. netstat – Linux network and statistics monitoring tool
netstat command displays network connections, routing tables, interface statistics, masquerade connections, and multicast memberships.
# netstat -tulpn
# netstat -nat
12. ss – Network Statistics
ss command use to dump socket statistics. It allows showing information similar to netstat. Please note that the netstat is mostly obsolete. Hence you need to use ss command. To ss all TCP and UDP sockets on Linux:
# ss -t -a
OR
# ss -u -a
Show all TCP sockets with process SELinux security contexts:
# ss -t -a -Z
See the following resources about ss and netstat commands:
•.ss: Display Linux TCP / UDP Network and Socket Information
•.Get Detailed Information About Particular IP address Connections Using netstat Command
13. iptraf – Get real-time network statistics on Linux
iptraf command is interactive colorful IP LAN monitor. It is an ncurses-based IP LAN monitor that generates various network statistics including TCP info, UDP counts, ICMP and OSPF information, Ethernet load info, node stats, IP checksum errors, and others. It can provide the following info in easy to read format:
•.Network traffic statistics by TCP connection
•.IP traffic statistics by network interface
•.Network traffic statistics by protocol
•.Network traffic statistics by TCP/UDP port and by packet size
•.Network traffic statistics by Layer2 address
Fig.02: General interface statistics: IP traffic statistics by network interface 
Fig.03 Network traffic statistics by TCP connectionInstall IPTraf on a Centos / RHEL / Fedora Linux To Get Network Statistics
14. tcpdump – Detailed network traffic analysis
tcpdump command is simple command that dump traffic on a network. However, you need good understanding of TCP/IP protocol to utilize this tool. For.e.g to display traffic info about DNS, enter:
# tcpdump -i eth1 'udp port 53'
View all IPv4 HTTP packets to and from port 80, i.e. print only packets that contain data, not, for example, SYN and FIN packets and ACK-only packets, enter:
# tcpdump 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
Show all FTP session to 202.54.1.5, enter:
# tcpdump -i eth1 'dst 202.54.1.5 and (port 21 or 20'
Print all HTTP session to 192.168.1.5:
# tcpdump -ni eth0 'dst 192.168.1.5 and tcp and port http'
Use wireshark to view detailed information about files, enter:
# tcpdump -n -i eth1 -s 0 -w output.txt src or dst port 80
15. iotop – Linux I/O monitor
$ sudo iotop
Sample outputs:
iotop monitoring linux disk read write IOLinux iotop: Check What’s Stressing And Increasing Load On Your Hard Disks
