30 Linux System Monitoring Tools Every SysAdmin Should Know
======
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:
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.
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.
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][4]
```
#### 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
### 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
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:
### 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 ][9]
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][12] information about files, enter:
`# tcpdump -n -i eth1 -s 0 -w output.txt src or dst port 80`
### 15. iotop - Linux I/O monitor
iotop command monitor, I/O usage information, using the Linux kernel. It shows a table of current I/O usage sorted by processes or threads on the server.
[Linux iotop: Check What's Stressing And Increasing Load On Your Hard Disks][14]
### 16. htop - interactive process viewer
htop is a free and open source ncurses-based process viewer for Linux. It is much better than top command. Very easy to use. You can select processes for killing or renicing without using their PIDs or leaving htop interface.
### 17. atop - Advanced Linux system & process monitor
atop is a very powerful and an interactive monitor to view the load on a Linux system. It displays the most critical hardware resources from a performance point of view. You can quickly see CPU, memory, disk and network performance. It shows which processes are responsible for the indicated load concerning CPU and memory load on a process level.
You must monitor process and login activity on your Linux server. The psacct or acct package contains several utilities for monitoring process activities, including:
1. ac command : Show statistics about users' connect time
2. [lastcomm command][17] : Show info about about previously executed commands
3. accton command : Turns process accounting on or off
4. sa command : Summarizes accounting information
[How to keep a detailed audit trail of what's being done on your Linux systems][18]
### 19. monit - Process supervision
Monit is a free and open source software that acts as process supervision. It comes with the ability to restart services which have failed. You can use Systemd, daemontools or any other such tool for the same purpose. [This tutorial shows how to install and configure monit as Process supervision on Debian or Ubuntu Linux][19].
### 20. nethogs- Find out PIDs that using most bandwidth on Linux
NetHogs is a small but handy net top tool. It groups bandwidth by process name such as Firefox, wget and so on. If there is a sudden burst of network traffic, start NetHogs. You will see which PID is causing bandwidth surge.
[Linux: See Bandwidth Usage Per Process With Nethogs Tool][21]
### 21. iftop - Show bandwidth usage on an interface by host
iftop command listens to network traffic on a given interface name such as eth0. [It displays a table of current bandwidth usage by pairs of host][22]s.
### 22. vnstat - A console-based network traffic monitor
vnstat is easy to use console-based network traffic monitor for Linux. It keeps a log of hourly, daily and monthly network traffic for the selected interface(s).
### 23. nmon - Linux systems administrator, tuner, benchmark tool
nmon is a Linux sysadmin's ultimate tool for the tunning purpose. It can show CPU, memory, network, disks, file systems, NFS, top process resources and partition information from the cli.
[Linux: Keep An Eye On Your System With Glances Monitor][29]
### 25. strace - Monitor system calls on Linux
Want to trace Linux system calls and signals? Try strace command. This is useful for debugging webserver and other server problems. See how to use to [trace the process and][30] see What it is doing.
### 26. /proc/ file system - Various Linux kernel statistics
/proc file system provides detailed information about various hardware devices and other Linux kernel information. See [Linux kernel /proc][31] documentations for further details. Common /proc examples:
```
# cat /proc/cpuinfo
# cat /proc/meminfo
# cat /proc/zoneinfo
# cat /proc/mounts
```
### 27. Nagios - Linux server/network monitoring
[Nagios][32] 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 alert when things go wrong and again when they get better. [FAN is][33] "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 easilly install a Nagios server. Added to this, a wide bunch of tools are including to the distribution, in order to improve the user experience around Nagios.
### 28. Cacti - Web-based Linux monitoring tool
Cacti is a complete network graphing solution designed to harness the power of RRDTool's data storage and graphing functionality. Cacti provides 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][34] tool under CentOS / RHEL.
### 29. KDE System Guard - Real-time Linux systems reporting and graphing
KSysguard is a network enabled task and system monitor application for KDE desktop. This tool can be run over 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][36] for detailed usage.
### 30. Gnome Linux system monitor
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.
![Fig.06 The Gnome System Monitor application][37]
* [lsof][39] - list open files, network connections and much more.
* [ntop][40] 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][41] - Another good monitoring tool for the X Window System. It is highly configurable and is able to 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][42] - It can be used to monitor the status of CPUs, main memory, hard disks, network interfaces, local and remote mailboxes, and many other things.
* [mtr][43] - mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.
* [vtop][44] - graphical terminal activity monitor on Linux
Did I miss something? Please add your favorite system motoring tool in the comments.
#### about the author
The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on [Twitter][45], [Facebook][46], [Google+][47].
[35]:https://www.cyberciti.biz/media/new/tips/2009/06/kde-systemguard-screenshot.png (Fig.05 KDE System Guard KDE task manager and performance monitor.)
[40]:https://www.cyberciti.biz/faq/debian-ubuntu-install-ntop-network-traffic-monitoring-software/ (Debian / Ubuntu Linux Install ntop To See Network Usage / Network Status)
