The following are some of the basic CLI, GUI, TUI commands to use in monitoring linux operated systems and helps in in-depth system analysis and debugging of server problems. These commands commonly help resolve issues regarding CPU, Memory, Network, and Storage.
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.
2: vmstat – System Activity, Hardware and System Information
The command vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.
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 testuser
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.
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 -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
Print Security Information
# ps -eo euser,ruser,suser,fuser,f,comm,label
# ps axZ
# ps -eM
See Every Process Running As User testuser
# ps -U testuser -u testuser 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=
# pgrep lighttpd
# pgrep -u testuser 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.
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).
8: sar – Collect and Report System Activity
The sar command is used to collect, report, and save system activity information. To see 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
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 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
11 netstat – Network Statistics
The command netstat displays network connections, routing tables, interface statistics, masquerade connections, and multicast memberships
12: ss – Network Statistics
ss command is used to dump socket statistics. It allows showing information similar to netstat.
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 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 eth0 'tcp port 80'
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&0xf)<<2)) - ((tcp&0xf0)>>2)) != 0)'
To display all FTP session to 188.8.131.52, enter:
# tcpdump -i eth1 'dst 184.108.40.206 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
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 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. See how to install 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 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 on linux box.
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 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.
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
- Installed memory
- Processors and speeds
- System Status
- Currently available disk space
- Memory and swap space
- Network usage
- File Systems
- Lists all mounted filesystems along with basic information about each.
More Tools of interest
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.
- wireshark - is a free and open-source packet analyzer. It is used for network troubleshooting, analysis, software and communications protocol development, and education. Originally named Ethereal, in May 2006 the project was renamed Wireshark due to trademark issues.
- snort – Snort’s open source network-based intrusion detection system (NIDS) has the ability to perform real-time traffic analysis and packet logging on Internet Protocol (IP) networks. Snort performs protocol analysis, content searching, and content matching. The program can also be used to detect probes or attacks, including, but not limited to, operating system fingerprinting attempts, common gateway interface, buffer overflows, server message block probes, and stealth port scans.
- Centreon – Centreon is an Open Source software package that lets you supervise all the infrastructures and applications comprising your information system.