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:
Finding out system bottlenecks
Disk (storage) bottlenecks
CPU and memory bottlenecks
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.
Commonly Used Hot Keys With top Linux monitoring tools
Here is a list of useful hot keys:
Displays summary information off and on.
Displays memory information off and on.
Sorts the display by top consumers of various system resources. Useful for quick identification of performance-hungry tasks on a system.
Enters an interactive configuration screen for top. Helpful for setting up top for a specific task.
Enables you to interactively select the ordering within top.
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:
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
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:
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
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&0xf)<<2)) - ((tcp&0xf0)>>2)) != 0)' Show all FTP session to 126.96.36.199, enter: # tcpdump -i eth1 'dst 188.8.131.52 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
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. $ htop Sample outputs:
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. $ atop
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. $ sudo nethogs Linux: See Bandwidth Usage Per Process With Nethogs Tool
21. iftop – Show bandwidth usage on an interface by host
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 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 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 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 “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 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.
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
Processors and speeds
Currently available disk space
Memory and swap space
Lists all mounted filesystems along with basic information about each.
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 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 – 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 – mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.
vtop – graphical terminal activity monitor on Linux
gtop – Awesome system monitoring dashboard for Linux/macOS Unix terminal
Did I miss something? Please add your favorite system motoring tool in the comments.