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20 Linux System Monitoring Tools That you should know

Need to monitor Linux server performance? Try these kinds of built-in commands as well as a few add-on tools. Most of the Linux distributions are equipped with tons of monitoring. These tools provide you with metrics that are available to secure information about system activities. You should utilize these kinds of tools to find the possible factors behind a performance problem. The commands discussed below are essentially the most basic commands when it comes to system analysis and debugging server issues such as:

  1. Finding out congestion.
  2. Disk (storage) tie-up.
  3. CPU and memory tie-up.
  4. Network congestion.
The Gnome System Monitor application


                         

via GIPHY



20: Gnome System Monitor – Real-time Systems Reporting and Graphing


The System Monitor application enables you to display basic system information and monitor system processes, usage of system resources, and file systems. You can also use System Monitor to modify the behavior of your system. Although not as powerful as the KDE System Guard, it provides the basic information which may be useful for new users: 

  • Displays various basic information about the computer’s hardware and software.
  • Linux Kernel version
  • GNOME version
  • Hardware
  • Installed memory
  • Processors and speeds
  • System Status
  • Currently available disk space
  • Processes
  • Memory and swap space
  • Network usage
  • File Systems
  • Lists all mounted filesystems along with basic information about each.


19: KDE System Guard – Real-time Systems Reporting and Graphing


KSysguard is a network-enabled task and system monitor application for KDE desktop. This tool can be run over the ssh session. It provides lots of features such as a client/server architecture that enables monitoring of local and remote hosts. The graphical front end uses so-called sensors to retrieve the information it displays. A sensor can return simple values or more complex information like tables. For each type of information, one or more displays are provided. Displays are organized in worksheets that can be saved and loaded independently from each other. So, KSysguard is not only a simple task manager but also a very powerful tool to control large server farms. See the KSysguard handbook for detailed usage.

KDE System Guard
Cacti – Web-based Monitoring Tool

18: Cacti – Web-based Monitoring Tool


Cacti is a complete network graphing solution designed to harness the power of RRDTool’s data storage and graphing functionality. Cacti provide a fast poller, advanced graph templating, multiple data acquisition methods, and user management features out of the box. All of this is wrapped in an intuitive, easy to use interface that makes sense for LAN-sized installations up to complex networks with hundreds of devices. It can provide data about network, CPU, memory, logged in users, Apache, DNS servers and much more. See how to install and configure Cacti network graphing tool under CentOS / RHEL.


17: Nagios – Server And Network Monitoring


Nagios is a popular open-source computer system and network monitoring application software. You can easily monitor all your hosts, network equipment and services. It can send an alert when things go wrong and again when they get better. FAN is “Fully Automated Nagios”. FAN goals are to provide a Nagios installation including most tools provided by the Nagios Community. FAN provides a CDRom image in the standard ISO format, making it easy to easily install a Nagios server. Added to this, a wide bunch of tools is including to the distribution, to improve the user experience around Nagios.

Nagios – Server And Network Monitoring

Proc file system – Various Kernel Statistics

16: /Proc file system – Various Kernel Statistics


/proc file system provides detailed information about various hardware devices and other Linux kernel information. See Linux kernel /proc documentations for further details. Common /proc examples:
# cat /proc/cpuinfo
# cat /proc/meminfo
# cat /proc/zoneinfo
# cat /proc/mounts


15: strace – System Calls


Trace system calls and signals. This is useful for debugging webserver and other server problems. See how to use to trace the process and see What it is doing.









14: tcpdump – Detailed Network Traffic Analysis


The tcpdump is a simple command that dumps traffic on a network. However, you need a good understanding of the TCP/IP protocol to utilize this tool. For.e.g to display traffic info about DNS, enter:
# tcpdump -i eth1 'udp port 53'

To display 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)'

To display all FTP session to 202.54.1.5, enter:
# tcpdump -i eth1 'dst 202.54.1.5 and (port 21 or 20'

To display 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


13: iptraf – Real-time Network Statistics


The iptraf command is an interactive colorful IP LAN monitor. It is a 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 a network interface
  • Network traffic statistics by protocol
  • Network traffic statistics by TCP/UDP port and by packet size
  • Network traffic statistics by Layer2 address
  •  

General interface statistics: IP traffic statistics by network interface

Network traffic statistics by TCP connection

Network traffic statistics by TCP connection


ss – Sockets Summary


12: ss – Sockets Summary

The ss command is used to show socket statistics. It can display stats for PACKET sockets, TCP sockets, UDP sockets, DCCP sockets, RAW sockets, Unix domain sockets, and more. It allows showing information similar to the netstat command.  It can display more TCP and state information than other tools. It is a new, incredibly useful and faster (as compare to netstat) tool for tracking TCP connections and sockets. SS can provide information about:
# ss -s
  • All TCP sockets.
  • All UDP sockets.
  • All established ssh / ftp / http / https connections.
  • All local processes connected to the X server.
  • Filtering by state (such as connected, synchronized, SYN-RECV, SYN-SENT, TIME-WAIT), addresses and ports.
  • All the TCP sockets in state FIN-WAIT-1 and much more.


11: netstat – Network Statistics


The command netstat displays network connections, routing tables, interface statistics, masquerade connections, and multicast memberships. ss command is used to dump socket statistics. It allows showing information similar to netstat.
# netstat -nat | awk '{print $6}' | sort | uniq -c | sort -n

netstat - Network Statistics

10: pmap – Process Memory Usage

The command pmap reports a memory map of a process. Use this command to find out the causes of memory bottlenecks.
# pmap -d PID
pmap – Process Memory Usage 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
  •  
=> Related:: Linux find the memory used by a program/process using pmap command 

9: mpstat – Multiprocessor Usage

The 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
=> Related:: Linux displays each multiple SMP CPU processors utilization individually.

sar – Collect and Report System Activity



8: sar – Collect and Report System Activity


The sar command is used to collect, report, and save system activity information. To see the network counter, enter:
# sar -n DEV | more

To display 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
=> Related:: How to collect Linux system utilization data into a file 


7: 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).
# iostat

Created with GIMP


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
=> Related: : Linux Track NFS Directory / Disk I/O Stats

free – Memory Usage


6: free – Memory Usage


The command free displays 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


5: ps – Displays The Processes

the 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 the 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


To See Threads ( LWP and NLWP)

# ps -AlFH


To See Threads After Processes

# ps -AlLm


Print All Process On The Server

# ps ax # ps axu


Print A Process Tree

# ps -ejH # ps axjf # pstree


Print Security Information

# ps -eo euser,ruser,suser,fuser,f,comm,label # ps axZ # ps -eM


See Every Process Running As User dcg

# ps -U dcg -u dcg u


Set 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


Display Only The Process IDs of Lighttpd

# ps -C lighttpd -o pid=
OR

# pgrep -u vivek php-cgi


Display The Name of PID 55977

# ps -p 55977 -o comm=


Find Out The Top 10 Memory Consuming Process

# ps -auxf | sort -nr -k 4 | head -10


Find Out top 10 CPU Consuming Process

# ps -auxf | sort -nr -k 3 | head -10



4: uptime – Tell How Long The System Has Been Running

uptime – Tell How Long The System Has Been Running
The 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 an 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.


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


2: vmstat – System Activity, Hardware and System Information

vmstat – System Activity, Hardware and System Information
The command vmstat 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


1: top – Process Activity Command

The top program 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. [/column][column sm=4] Linux top command


                                                       

via GIPHY


Commonly Used Hot Keys

The top command provides several useful hotkeys:
Hot KeyUsage
tDisplays summary information off and on.
mDisplays memory information off and on.
ASorts the display by top consumers of various system resources. Useful for quick identification of performance-hungry tasks on a system.
fEnters an interactive configuration screen for the top. Helpful for setting up top for a specific task.
oEnables you to interactively select the ordering within the top.
rIssues renice command.
kIssues kill command.
zTurn on or off-color/mono


Bonus:

  • Nmap – scan your server for open ports.
  • lsof – list open files, network connections and much more.
  • ntop web-based tool – ntop is the best tool to see network usage in a way similar to what top command does for processes i.e. it is network traffic monitoring software. You can see network status, protocol wise distribution of traffic for UDP, TCP, DNS, HTTP, and other protocols.
  • Conky – Another good monitoring tool for the X Window System. It is highly configurable and can monitor many system variables including the status of the CPU, memory, swap space, disk storage, temperatures, processes, network interfaces, battery power, system messages, e-mail inboxes, etc.
  • GKrellM – It can be used to monitor the status of CPUs, main memory, hard disks, network interfaces, local and remote mailboxes, and many other things.
  • vnstat – vnStat is a console-based network traffic monitor. It keeps a log of hourly, daily and monthly network traffic for the selected interface(s).
  • htop – htop is an enhanced version of the top, the interactive process viewer, which can display the list of processes in a tree form.
  • mtr – mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.

                                                                 

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Credit to the owner of this listed information: Cyberciti.biz


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Kris Lacanlale

Hey! I'm Kris. A Dream Catcher collector, your tech-savvy sassy girl behind Dream Catcher Girl, a fur-parents and married while waiting for our super baby to come! Come along with me as I strive to live a life I love to do creatively and chic.