All Linux Monitoring Commands for every Linux User

Filed under Linux and Unix by on September 12, 2010 at 2:15 pm {no comments}

This article provides information related to Top Linux Monitoring Tools and Linux Commands which can also be used to measure linux Performance and CPU utilization.

Most Linux distributions are equipped with tons of monitoring. 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 basic commands when it comes to system analysis and debugging server issues such as:

  1. Finding out bottlenecks.
  2. Disk (storage) bottlenecks.
  3. CPU and memory bottlenecks.
  4. Network bottlenecks.

#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 hot keys:

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

#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

#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
# 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 report 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 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 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:

SS Command in Linux

Netstat Command in Linux

#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 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'

#15: strace – System Calls

Trace system calls and signals. This is useful for debugging webserver and other server problems.

#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

Netstat Command in Linux

Filed under Linux and Unix by on September 12, 2010 at 2:11 pm {no comments}

netstat command and shell pipe feature can be used to dig out more information about particular IP address connection. You can find out total established connections, closing connection, SYN and FIN bits and much more. You can also display summary statistics for each protocol using netstat.

This is useful to find out if your server is under attack or not. You can also list abusive IP address using this method.
# netstat -nat | awk '{print $6}' | sort | uniq -c | sort -n

Dig out more information about a specific ip address:
# netstat -nat |grep {IP-address} | awk '{print $6}' | sort | uniq -c | sort -n

      2 LAST_ACK
      2 LISTEN
      4 FIN_WAIT1
     14 ESTABLISHED
     91 TIME_WAIT
    130 FIN_WAIT2

Busy server can give out more information:
# netstat -nat |grep 202.54.1.10 | awk '{print $6}' | sort | uniq -c | sort -n

Get List Of All Unique IP Address

To print list of all unique IP address connected to server, enter:
# netstat -nat | awk '{ print $5}' | cut -d: -f1 | sed -e '/^$/d' | uniq
To print total of all unique IP address, enter:
# netstat -nat | awk '{ print $5}' | cut -d: -f1 | sed -e '/^$/d' | uniq | wc -l

Find Out If Box is Under DoS Attack or Not

If you think your Linux box is under attack, print out a list of open connections on your box and sorts them by according to IP address, enter:
# netstat -atun | awk '{print $5}' | cut -d: -f1 | sed -e '/^$/d' |sort | uniq -c | sort -n

Display Summary Statistics for Each Protocol

Simply use netstat -s:
# netstat -s | less
# netstat -t -s | less
# netstat -u -s | less
# netstat -w -s | less
# netstat -s

Display Interface Table

You can easily display dropped and total transmitted packets with netstat for eth0:
# netstat --interfaces eth0

SS Command in Linux

Filed under Linux and Unix by on September 12, 2010 at 2:05 pm {one comment}

The ss command is used to dump socket statistics. It allows showing information similar to 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:

  • All TCP sockets.
  • All UDP sockets.
  • All established ssh / ftp / http / https connections.
  • All local processes connected to X server.
  • All the tcp sockets in state FIN-WAIT-1 and much more.

Most Linux distributions are shipped with ss and many monitoring tools. Being familiar with this tool helps enhance your understand of what’s going on in the system sockets and helps you find the possible causes of a performance problem.

Task: Display Sockets Summary

List currently established, closed, orphaned and waiting TCP sockets, enter:
# ss -s
Sample Output:

Total: 734 (kernel 904)
TCP:   1415 (estab 112, closed 1259, orphaned 11, synrecv 0, timewait 1258/0), ports 566

Transport Total     IP        IPv6
*	  904       -         -
RAW	  0         0         0
UDP	  15        12        3
TCP	  156       134       22
INET	  171       146       25
FRAG	  0         0         0

Task: Display All Open Network Ports

# ss -l
Sample Output:

ss -l
Recv-Q Send-Q                                                  Local Address:Port                                                      Peer Address:Port
0      0                                                           127.0.0.1:smux                                                                 *:*
0      0                                                           127.0.0.1:10024                                                                *:*
0      0                                                           127.0.0.1:10025                                                                *:*
0      0                                                                   *:3306                                                                 *:*
0      0                                                                   *:http                                                                 *:*
0      0                                                                   *:4949                                                                 *:*
0      0                                                                   *:domain                                                               *:*
0      0                                                                   *:ssh                                                                  *:*
0      0                                                                   *:smtp                                                                 *:*
0      0                                                           127.0.0.1:rndc                                                                 *:*
0      0                                                           127.0.0.1:6010                                                                 *:*
0      0                                                        	   *:https                                                                *:*
0      0                                                                  :::34571                                                               :::*
0      0                                                                  :::34572                                                               :::*
0      0                                                                  :::34573                                                               :::*
0      0                                                                 ::1:rndc                                                                :::*

Type the following to see process named using open socket:
# ss -pl
Find out who is responsible for opening socket / port # 4949:
# ss -lp | grep 4949
Sample output:

0      0                            *:4949                          *:*        users:(("munin-node",3772,5))

munin-node (PID # 3772) is responsible for opening port # 4949. You can get more information about this process (like memory used, users, current working directory and so on) visiting /proc/3772 directory:
# cd /proc/3772
# ls -l

Task: Display All TCP Sockets

# ss -t -a

Task: Display All UDP Sockets

# ss -u -a

Task: Display All Established SMTP Connections

# ss -o state established '( dport = :smtp or sport = :smtp )'

Task: Display All Established HTTP Connections

# ss -o state established '( dport = :http or sport = :http )'

Task: Find All Local Processes Connected To X Server

# ss -x src /tmp/.X11-unix/*

Task: List All The Tcp Sockets in State FIN-WAIT-1

List all the TCP sockets in state -FIN-WAIT-1 for our httpd to network 202.54.1/24 and look at their timers:
# ss -o state fin-wait-1 '( sport = :http or sport = :https )' dst 202.54.1/24

All Languages Technical Interview Questions

Filed under Interview questions by on March 6, 2010 at 3:47 pm {one comment}

This technical presentation is collection of Technical Interview questions. This Technical Aptitude contains C language Aptitude, Data Structures Aptitude,C++ Aptitude and OOPS Interview Questions.

All Languages Interview Questions

Get all Interview Questions at one place in this article. You will get complete Technical Interview questions and answers which are most frequently asked in Interviews. These Interview questions will be very useful in your future interviews. For each question, there are solutions available. So there is no need to refer to other websites for solutions.

Do comment if you like the post and add some valuable links if you find any better and similar to this article.

Data Structures Aptitude

scp command in unix

Filed under Interview questions, Linux and Unix by on June 3, 2009 at 1:13 pm {no comments}

Now here is an simple command in unix to copy the files from one linux machine to other linux machine easily.

scp root@:

Now if you have more files, you cannot copy all files using scp , first a tar has to be made and then tar has to be copied and then it should be untarred.

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