20 Linux System Monitoring Tools

Wed 30 2011

20 Linux System Monitoring Tools

by bernt & torsten

Need to monitor Linux server performance? Try these built-in commands and a few add-on tools. Most Linux distributions are equipped with tons of monitoring. You can use these tools to find the possible causes of a performance problem.

#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.

Commonly Used Hot Keys

The top command provides several useful hotkeys:

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 the top. Helpful for setting up top for a specific task.
o	Enables you to interactively select the ordering within the top.
r	Issues renice command.
k	Issues kill command.
z	Turn on or off colour/mono

#2: vmstat – System Activity, Hardware and System Information

The command vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.
# vmstat 3

Display Memory Utilization Slabinfo

# vmstat -m

Get Information About Active / Inactive Memory Pages

# vmstat -a

#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

#4: 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

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 Processes

ps command will report a snapshot of the current processes. To select all processes use the -A or -e option:
# ps -A

ps is just like top but provides more information.

Show Long Format Output

# ps -AlTo 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 Vivek

# ps -U vivek -u vivek 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 lighttpd
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

#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

#7: iostat – Average CPU Load, Disk Activity

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

#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 | moreTo display the network counters from the 24th:
# sar -n DEV -f /var/log/sa/sa24 | moreYou can also display real-time usage using sar:
# sar 4 5

#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

#10: pmap – Process Memory Usage

The command pmap report the memory map of a process. Use this command to find out the causes of memory bottlenecks.
# pmap -d PIDTo display process memory information for pid # 47394, enter:
# pmap -d 47394

#11 and #12: netstat and ss – 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. See the following resources about ss and netstat commands:

#13: iptraf – Real-time Network Statistics

The 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

#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 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 sessions 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'

#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.

#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

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 alerts when things go wrong and again when they get better. FAN is a “Fully Automated Nagios”. FAN’s 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 are including in the distribution, in order to improve the user experience around Nagios.

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.

#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 ssh sessions. 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.

#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 behaviour 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.

Bonus: Additional Tools

A few more tools:

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 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.
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 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.