Linux Commands Documentation

Linux Commands Documentation

Starting with A

# a2ps- Formats files for printing on a PostScript printer
# AMSTeX- formatting documents with TeX, AMS version
# AMSLaTeX- AMS version of LaTeX
# at- allows you to run programs at a later date
# awk- pattern scanning and string manipulation language, developed by GNU. See also mawk, a POSIX implementation of awk

Starting with B

# bash- The bourne again shell, one of the two basic ways you interact with the computer, the other is the tcsh shell
# bc- an arbitrary precision calculator. If you want a calculator for X-windows try xcalc
# bibtool- BibTeX file manipulation tool
# bison- the YACC-compatible Parser Generator
# bzip2- a file compressor

Starting with C

# cdrecord- record audio and data Compact Discs. There is also a graphical program called xcdroast
# chmod- to change permissions of files
# chown- to change ownership of files
# chktex- finds LaTeX errors
# cjpeg- compress an image file to a JPEG file
# clisp- common Lisp language interpreter
# cmp- compares two files.
# convert- converts between different formats of image files
# cpio- copy files to and from archives
# cp- to copy one file into another
# cpp- the GNU C preprocessor
# cron- to run programs periodically (as opposed to at, which run them just once); this link contains the format of the control file.
# csh- the C shell

Starting with D

# date- shows (and sets up, for the super user) the system date
# dc- an arbitrary precision calculator; see also bc
# ddd- Data Display Debugger, the debugger for gcc (GNU C compiler)
# diff- shows the differences bewteen two files; see tkdiff for a graphical program that does a similar job and zdiff to look at differences between compressed files
# dqs- a batch queueing system that allows to queue jobs (programs) in different machines to be run according to the load of the machines. You can check also reference guide. See also queue
# dvips- converts files from TeX DVI format to PostScript

Starting with E

# elm- a program to read/send email for UNIX:
# emacs- the GNU editor where all started… There is a similar program for X-windows (graphical interface) called xemacs
# expect- a toolf fo rautomating interactive applications such as telnet, ftp, rlogin, etc (the Frequently Asked Question file)
# egrep- searches one or more input files for lines containing a match to a specified pattern

Starting with F

# flex- fast lexical analyzer generator, or a tool for generating programs that performs patter-matching on tex.
# ftp- the File Transfer Program, that allows the transfer of file between computers connected to the Internet (or some sort of network)
# find- searchs for files in a directory
# free- show how much memory is being used and how much is free in the system
# fromdos- converts a file from DOS format to UN*X format; the reverse process is done with todos
# fvwm95- a X-windows manager that will make your computer look like Windows’95: here you have an example of a configuration file

Starting with G

# g++ – the GNU C++ compiler (it is also the GNU C compiler)
# gimp- an image manipulation and paint program
# g77- the GNU Fortran compiler
# gawk-same as awk above
# gcc- the GNU C compiler
# giftrans- allows to put transparent or background colors on GIF files
# gmp- the GNU multiple precision arithmetic library, to write C programs with arbitrary precision
# grep- same as egrep above
# gdb- Data Display Debugger, same as ddd above
# gs- a PostScript and PDF language interpreter and previewer
# gsl- the GNU Scientific Library, for writting programs in C
# gv- a previewer for PostScript and PDF files
# gzip- compress files

Starting with H

# hcc- a brief reference to C/C++ compiler for LAM (parallel compiling)
# head- show the beginning (head) of a file
# hexdump- gives the hexademic format of files in the computer
# host- a program to find addresses (and other data) of computers connected to the Internet

Starting with I

# indent- a program that makes C code easier to read and converts from one style of writing C (eg. GNU, Kernighan & Ritchie, Berkeley) to another
# Imagemagick- a program to display and manipulate image files
# imake- the make command for X11 (manual page formatted on html)
ispell, a spell checker
# imp- a program to read your mail via a web browser (like Netscape)

Starting with K

# kill- stops processes running in a computer
# killall- kills processes by name

Starting with I

# latex- to format documents, especially mathematics; quite complete user’s guide. If you want to find a particular symbol you can check this table of LaTeX symbols
# latex2html- converts from LaTeX to HTML (web based files)
# less- a command to look a files (a PAGER, in UN*x language)
# lpq- the command to look at the printer queue
# lpr- the command to print
# ls- to list contents and information of files and directories
# lynx- a text-based browser, useful for example for pages with too many graphics or bad Java scripts (or if you want fast browsing)

Starting with M

# magma- a Computer Algebra system for solving problems in algebra, number theory, geometry and combinatorics (works only in prime). For the full documentation you can start with link
# mailx- the basic UNIX command to send/read mail
# make- a tool to generate execuatable files from a program’s source files
# man- the program to look at manual (help) pages of Linux/UN*X commands
# mathematica- a commercial program for mathematical computations
# maple- another commercial program for doing mathematical computations
# mawk- an implementation of awk (pattern scanning and string manipulation language) that tries to follow the POSIX standard. See also awk, the GNU implementation of awk
# mc- the Midnight Commander, a directory/file manager for UN*X operating systems
# mkisofs- program used to create file systems to later write them on CDs
# montage- creates a composite image by combining several separate images
# more- a program that allows you to look at files (like less, but no so powerful)
# mtools- a set of programs that allows you to handle DOS files and directories, in particular floppy disks. The most common commands are the following:
# mcd- to change directories
# mcopy- to copy between DOS and Linux files
# mdel- to delete DOS files
# mdir- to make DOS directories
# mdu- to check the usage of DOS files in a floppy/file system
# mformat- to format a floppy to be used as DOS floppy later
# mv- renames files

Starting with N
# ncftp- a powerful interface for using ftp (File Transfer Protocol)
# newalias- install new elm aliases
# nice- makes processes to run on low priority so the system can do more impotant tasks. If the process is already running you can use the command renice
# nsloopup- a program to find addresses (and other data) of machines connected to the Internet. Note: better use the program “host” as this program might disappear in the future

Starting with P

# pari- software package for computer-aided number theory, consisting of a C library (to write your own programs) and an interactive calculator called gp
# pdflatex- produces PDF output (instead of standard dvi file) from a LaTeX file
# pdftex- produces PDF output (instead of standard dvi file) from a TeX file. You can check a sample document here
# pdftops- converts PDF (Portable Document Format) files to PostScript so they can be printed.
# pftp- the same as ftp but called in a “passive” way, good for example when two computers are connecting with firewall between them.
# pico- a simple editor that comes with the “pine” package
# pilot- a file browser in the style of “pine”
# pine- a popular program to read email. The documentation for the latest version (“pine 4”) is available: pine4. Check also elm, another popular email program.
# pmake- a version of make, that is, a tool to generate execuatable files from a program’s source files
# ps2pdf- converts PS files to PDF files
# psselect- select pages from a PS file (for example, to print only certain number of pages)
# psbook- arranges pages in a PS file so the print out looks like a book

Starting with Q

# queue- allows to queue jobs (programs) in different machines to be run according to the load of the machines. See also dqs
# quota- displays users’ disk usage and limits

Starting with R

# rcs- Revision Control System, a program that allows you to keep different versions of a file/document in a single “control” file; good, for example, when you are editing a file very frequently and do not want to have too many files with similar names
# renice- to change priority of running processes, so they can be slowed down allowing the system to work faster on more important tasks. You can look at the information about nice command that allows you to start a process with low priority.
# rm- deletes files
# rsh- remote shell, allows you to login or execute programs in a remote computer

Starting with S

# scanimage- a simple command-line (no graphical interface) program to interact with a scanner. See also
# xscanimage- the command with graphical interface
# sendfile- a program to send files via Internet
# setterm- changes the properties of the terminal (“screen”), like number of lines/rows, automatic line wrap, etc
# shar- creates shell archives (shar files); these are packed files that can be unpacked later in a simple way bu executing a command. The packed files can be send by email
# sleep- delays for a specified amount of time (it does nothing for some time, hence the name of the program)
# sort- sorts lines in a text file
# spell- a UN*X spell emulator, simpler and less powerful than ispell
# split- splits a file into smaller files, good for example to send small files by email
# ssh- the Secure Shell, allows you to execute commands or login in a remote computer in a secure (crypted) way. It should be prefereed to the rather equivalent, non-secure, rsh

Starting with T
# tail- shows the end (tail) of a file
# tar- a program to create and manipulate archives (“tar files”) which are actually collections of many other files
# tcsh- a very popular shell (that is, the basic program that allows you to execute commands, and it is the one you run after login in the system). An example of a configuration file can be found here. The other popular shell is bash
# tee- reads from standard input (basically keyboard or a file) and writes to standard output (screen) and files; good if you want to write something to a file and see what is written at the same time
# telnet- allows you to log on in a computer conneted to the Internet or a local network
# telnet-ssl- like telnet above but with crypted communication, to increase security
TeX, to typeset mathematical documents; this is the manual page of the command “tex”; there is lot of documentation in the Internet
# time- runs programs and tells how much time (real time and computer usage) they take
# tkdesk- a Graphical File and Desktop Manager for X-windows
# tkdiff- this program displays in a nice, graphical way, the differences between two files
# tkdvi- a dvi previewer based on tcl/tk, adds some features to the standard dvi previewers like xdvi
# todos- converts a file from UN*X format to DOS format; the reverse process is done with fromdos
# top- shows processes running, displaying the most CPU-intensive tasks, and allows renice and kill them
# touch- allows to change the timestamps of files
# traceroute- finds the route that packets take between your computer and another computer connected to the Internet or a local network. It might not work if your computer is behind a firewall that does not allow ping (for security reasons)
# transfig- creates a make file to translate figures in FIG code to LaTeX
# tree- lists all the files in a directory in a tree-like format

Starting with U

# uname- gives information about the machine you are working on, like hardaware type, name, processor, operating system.
# uname- gives information about the machine you are working on, like hardaware type, name, processor, operating system…
# untex- removes LaTeX commands from a file
# unzip- extracts or lists the files in a “qip” archive (a type of file that has many files within it)
# uuencode- puts a binary file in an encoded format so it can be sent over email as a simple text file; the reverse process is done with uudecode. Nowadays most mail programs can do similar things via MIME without need for the user to do any extra processing
# untex- removes LaTeX commands from a file
# unzip- extracts or lists the files in a “qip” archive (a type of file that has many files within it)
# uuencode- puts a binary file in an encoded format so it can be sent over email as a simple text file; the reverse process is done with uudecode. Nowadays most mail programs can do similar things via MIME without need for the user to do any extra processing

Starting with V

# vacation- returns a message to senders of an email telling them that you are currently not reading your mail (“on vacation”)
# vi- the classical (and for some people obsure) UN*X editor; if you want a more advanced help you can check this document. Other editors are emacs, pico and xemacs
# vlock- a program to lock one or more sessions on the Linux console

Starting with W

# w- shows who is logged in a computer and what they are doing
# wall- writes a message to all users logged on in a computer
# wc- computes the number of bytes, words and lines in files
# wdiff- displays word differences between text files
# wget- a command to get files from the World Wide Web without using a browser (that is, without netscape, lynx, etc, just a plain command)
# whiptail- display graphical boxes from scripts
# workman- a graphical program to play audio compact discs

Starting with X

# xcal- calendar with alarms and a notebook for X-windows
# xcalc- a scientific calculator for X-windows. See also bc, an arbitrary precision calculator program
# xcdroast- a graphical program to write CDs. See also the more basic, command-line program cdrecord
# xclock- a digital/analog clock for X-windows
# xcolors- displays all the X-windows colors names
# xcolorsel- displays all the X-windows colors names in many formats
# xemacs- a version of emacs for X-windows. You can also access two documentation files in PDF format: the new users’ guide and the more advanced users’ guide
# xfig- a tool to create figures under X-windows (that can be later included in LaTeX files, for example). You can also access the same documentation in a fancier format (frames)
# xfontsel- a program to help you to select fonts for X-windows
# xfreecd- a X-windows program that looks like the frontpanel of a CD player and, as you might expect, plays audio CDs
# xhost- this program is used to add/delete hosts/users names authorised to display windows in your computer
# xlock- program to lock your X-windows session
# xmake- another make utility; check also imake and make
# xman- displays manual pages in a windows environment
# xmcpustate- shows usage of CPU
# xpaint- a graphics program to draw pictures under X-windows; you can save the files in many different formats (including gif and jpeg)
# xpdf- a program to display PDF files; see also gv
# xscanimage- a graphics-based command to use a scanner; see scanimage for a non-graphics command.
# xset- sets preferences for X-windows sessions
# xsysinfo- displays technical information about memory, CPU and other stuff in your machine
# xterm- the “basic” X-windows programs, like a shell, from which you can call any other program
# xxgdb- Data Display Debugger in for X-windows

Starting with Y

# yppasswd- the basic command to change your password in our system (or any system running NIS)
# ytree- a basic file manager that displays the files in a directory in a tree-like form. See also the Midnight Commander

Starting with Z

# zcat- allows you to look at a compressed file
# zdiff- shows differences between two compressed files; see also diff for looking at differences between two “regular” files and tkdiff for a nice graphical program that shows differencese between two “regular” files
# zip- creates ZIP archives, that is files that contain other files inside; see also tar and cpio, two programs that create archives

Note- Welcome all emails/calls from any readers with suggestions, new comments, & corrections at [email protected]

10 most used Linux Distributions

10 most used Linux Distributions

1. Ubuntu: This is probably the most user-friendly Linux distribution ever made. It’s very well done. Some power users don’t like it because they say its “too user friendly”, but most people seem to be very happy with it. I have used several different versions of Ubuntu, and I have nothing bad to say about it. This is a great distro.

Now stop reading, and go download one (if not all) of these Linux distributions. Are you still running Windows? Why? Linux is free and it’s better.

2. CentOS: Previous to Fedora, Red Hat made one Linux distro, it was simply called Red Hat Linux, and it was free. Later they split their efforts into two distros, Fedora, and RHEL (Red Hat Enterprise Linux). Fedora is still free, but RHEL has to be licensed. CentOS is the unofficial free version of RHEL. It is not supported by Red Hat, but has the same code base.

3. Fedora: Red Hat’s open project, Fedora, has long been a favorite of Linux users worldwide. Started in 2003, it is their free alternative to RHEL. While RHEL is marketed at enterprises, Fedora is targeted at home users, with a slightly different look and feel.

4. OpenSUSE: This is one of my personal favorites. I’ve always love the SUSE interface. The first version of SUSE that I used was version 8, and it was this distro that made me realize how cool Linux really was. SUSE was acquired by Novell in 2003. Shortly after the acquisition, they followed the “Red Hat Model” and split their offerings in two. OpenSUSE is the free version of Novell’s SUSE Linux Enterprise platform.

5. Debian: This is a solid distro! Period.

6. Mandriva: Years ago, this distro was called Linux Mandrake. This was one of the first Linux distros marketed at everyday users. It is very easy to use. I installed it several years ago, but haven’t used it recently.

7. Linux Mint: I’ve never used this one, but I’ve heard nothing but good things about it. The interface looks very slick and intuitive. I’m anxious to try it out.

8. PCLinuxOS: Next to Ubuntu (scroll down a bit to read about Ubuntu), this is probably the most user-friendly Linux distribution. In some ways, its actually more friendly than Ubuntu. This is a great distro for newcomers!

9. Slackware: This one has been around longer than any other Linux distro, since 1992. It’s marketed mostly at power users because its interface is less friendly than some of the others, but it is still a rock solid distro! It has certainly stood the test of time.

10. Gentoo: I installed this several years ago. It was the most customizable version of Linux I’d ever seen. The installer actually complied the source code specifically for your computer. It was so meticulous it was almost annoying. I hear they’ve changed this in recent releases though. It remains a very popular distro.

What is Distro (plural Distros) ?
(Internet, software) A set of software components, typically (but not necessarily) open source components, that have been packaged into a larger product or component for distribution to end-users. A shortened version of the word “distribution.” Distro means a version of Gnu&Linux or other OpenSource Operating System although some people would argue that the term should include the various Windows and Apple OSes

Most Used Linux System Monitoring Tools Every Linux Admin Should Know

Most Linux System Monitoring Tools Every Linux Admin Should Know

1. Ping IP Address/ Website
To check that IP address or website accessible or not.

2. setup
To change admin tools

3. 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.

The top command provides several useful hot keys:

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 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/mono

=> Related: How do I Find Out Linux CPU Utilization?

4. vmstat – System Activity, Hardware and System Information

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

Sample Outputs:

procs ———–memory———- —swap– —–io—- –system– —–cpu——
r b swpd free buff cache si so bi bo in cs us sy id wa st
0 0 0 2540988 522188 5130400 0 0 2 32 4 2 4 1 96 0 0
1 0 0 2540988 522188 5130400 0 0 0 720 1199 665 1 0 99 0 0
0 0 0 2540956 522188 5130400 0 0 0 0 1151 1569 4 1 95 0 0
0 0 0 2540956 522188 5130500 0 0 0 6 1117 439 1 0 99 0 0
0 0 0 2540940 522188 5130512 0 0 0 536 1189 932 1 0 98 0 0
0 0 0 2538444 522188 5130588 0 0 0 0 1187 1417 4 1 96 0 0
0 0 0 2490060 522188 5130640 0 0 0 18 1253 1123 5 1 94 0 0
Display Memory Utilization Slabinfo

# vmstat -m

Get Information About Active / Inactive Memory Pages

# vmstat -a

=> Related: How do I find out Linux Resource utilization to detect system bottlenecks?

5. 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
root pts/0 14:55 5.00s 0.04s 0.02s vim /etc/resolv.conf
root pts/1 17:43 0.00s 0.03s 0.00s w

6. 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


18:02:41 up 41 days, 23:42, 1 user, load average: 0.00, 0.00, 0.00
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.

7. 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

Sample Outputs:

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

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=

# pgrep lighttpd

# 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

8. Fdisk

9. 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

Sample Outputs:

Linux 2.6.18-128.1.14.el5 ( 06/26/2009
avg-cpu: %user %nice %system %iowait %steal %idle
3.50 0.09 0.51 0.03 0.00 95.86
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 22.04 31.88 512.03 16193351 260102868
sda1 0.00 0.00 0.00 2166 180
sda2 22.04 31.87 512.03 16189010 260102688
sda3 0.00 0.00 0.00 1615 0
=> Related: : Linux Track NFS Directory / Disk I/O Stats

10. 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

Sample Outputs:

Linux 2.6.18-128.1.14.el5 ( 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
=> Related: : How to collect Linux system utilization data into a file

11. 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

Sample Output:

Linux 2.6.18-128.1.14.el5 ( 06/26/2009
06:48:11 PM CPU %user %nice %sys %iowait %irq %soft %steal %idle intr/s
06:48:11 PM all 3.50 0.09 0.34 0.03 0.01 0.17 0.00 95.86 1218.04
06:48:11 PM 0 3.44 0.08 0.31 0.02 0.00 0.12 0.00 96.04 1000.31
06:48:11 PM 1 3.10 0.08 0.32 0.09 0.02 0.11 0.00 96.28 34.93
06:48:11 PM 2 4.16 0.11 0.36 0.02 0.00 0.11 0.00 95.25 0.00
06:48:11 PM 3 3.77 0.11 0.38 0.03 0.01 0.24 0.00 95.46 44.80
06:48:11 PM 4 2.96 0.07 0.29 0.04 0.02 0.10 0.00 96.52 25.91
06:48:11 PM 5 3.26 0.08 0.28 0.03 0.01 0.10 0.00 96.23 14.98
06:48:11 PM 6 4.00 0.10 0.34 0.01 0.00 0.13 0.00 95.42 3.75
06:48:11 PM 7 3.30 0.11 0.39 0.03 0.01 0.46 0.00 95.69 76.89
=> Related: : Linux display each multiple SMP CPU processors utilization individually.

12. 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

Sample Outputs:

47394: /usr/bin/php-cgi
Address Kbytes Mode Offset Device Mapping
0000000000400000 2584 r-x– 0000000000000000 008:00002 php-cgi
0000000000886000 140 rw— 0000000000286000 008:00002 php-cgi
00000000008a9000 52 rw— 00000000008a9000 000:00000 [ anon ]
0000000000aa8000 76 rw— 00000000002a8000 008:00002 php-cgi
000000000f678000 1980 rw— 000000000f678000 000:00000 [ anon ]
000000314a600000 112 r-x– 0000000000000000 008:00002
000000314a81b000 4 r—- 000000000001b000 008:00002
000000314a81c000 4 rw— 000000000001c000 008:00002
000000314aa00000 1328 r-x– 0000000000000000 008:00002
000000314ab4c000 2048 —– 000000000014c000 008:00002
00002af8d48fd000 4 rw— 0000000000006000 008:00002
00002af8d490c000 40 r-x– 0000000000000000 008:00002
00002af8d4916000 2044 —– 000000000000a000 008:00002
00002af8d4b15000 4 r—- 0000000000009000 008:00002
00002af8d4b16000 4 rw— 000000000000a000 008:00002
00002af8d4b17000 768000 rw-s- 0000000000000000 000:00009 zero (deleted)
00007fffc95fe000 84 rw— 00007ffffffea000 000:00000 [ stack ]
ffffffffff600000 8192 —– 0000000000000000 000:00000 [ anon ]
mapped: 933712K writeable/private: 4304K shared: 768000K
The last line is very important:

mapped: 933712K total amount of memory mapped to files
writeable/private: 4304K the amount of private address space
shared: 768000K the amount of address space this process is sharing with others
=> Related: : Linux find the memory used by a program / process using pmap command

13. netstat -rn

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: Display Linux TCP / UDP Network and Socket Information
Get Detailed Information About Particular IP address Connections Using netstat Command

14. 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

Fig.02: General interface statistics: IP traffic statistics by network interface

Fig.03 Network traffic statistics by TCP connection

15. 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, enter:
# tcpdump -i eth1 ‘dst and (port 21 or 20’

To display all HTTP session to
# tcpdump -ni eth0 ‘dst 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

16. 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.

17. /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

18. 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.

19. 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 under CentOS / RHEL.

20. 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.

How to Install & Configure Nagios On CENTOS/RHEL/FEDORA

Nagios is one of the popular open source system and network monitoring software application.Nagios let us monitor our IT infrastructure, be it servers, routers, switches or other devices.It monitor hosts and services and then alerting users when something wrong has been triggered. It is the powerful monitoring system that enables organizations to identify and manage IT infrastructure problems before they effect critical business processes.

Step to Install & Configuration


During portions of the installation you’ll need to have root access to your machine.

Make sure you’ve installed the following packages on your Fedora installation before continuing.

GCC compiler
GD development libraries

1- First install some tools : httpd, gcc, glib, glibc-common, gd and gd-devel

#yum install httpd php
#yum install gcc
#yum install glibc glibc-common
#yum install gd gd-devel

2- Create nagios user :

#/usr/sbin/useradd -m nagios
#passwd nagios
3- Add nagcmd group
#/usr/sbin/groupadd nagcmd
#/usr/sbin/usermod -a -G nagcmd nagios
#/usr/sbin/usermod -a -G nagcmd apache
4- Now go to download files .

nagios-3.1.0.tar.gz nagios-plugins-1.4.13.tar.gz nrpe-2.12.tar.gz

#tar -zxvf nagios-3.1.0.tar.gz
#cd nagios-3.1.0
./configure –with-command-group=nagcmd
#make all; make install; make install-init; make install-config; make install-commandmode; make install-webconf
5- Edit your email admin address :

Go to

vi /usr/local/nagios/etc/objects/contacts.cfg

6- Create a nagiosadmin account for logging into the Nagios web interfaceassign to this you’ll need it later.

#htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
enter the password.

7- Restart the httpd server :

#Service httpd restart
The second step : Extract and install plugins
1- Go to you downloaded nagios tools

#tar -zxvf nagios-plugins-1.4.13.tar.gz
2- cd nagios-plugins

./configure –with-nagios-user=nagios –with-nagios-group=nagios
make; make install
3- Now you have to add nagios to Chkconfig

chkconfig –add nagios
#chkconfig nagios on
4- Verify if you have a good config of nagios with the command

#/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
5- Check if there are no errors displayed; then start nagios with command :

#service nagios start
To simplify the procesure please disable the selinux and iptables and ip6tables

now open your browser and http://localhost/nagios orr http://ip/nagios

Click on Screen-shots

Redhat/CentOS Mail Server Setup: Postfix, Dovecot, Virtual users, MySQL, SASL, Postfixadmin, TLS

Redhat/CentOS Mail Server Setup: Postfix, Dovecot, Virtual users, MySQL, SASL, Postfixadmin, TLS

This is a small guide, showing how to install postfix, dovecot and postfixadmin on a server running CentOS.

The components of an e-mail server are:
the delivery and reception service – Postfix, which handles mail delivery
the mail retrieval service, dovecot, which handles POP3 and/or IMAP mail retrieval
users database, storing usernames, passwords, mail location. In this guide, i’ll use a mysql database for this task
the SMTP authentication mechanism, to make possible e-mail delivery for roaming users.
the management interface: Postfixadmin. This is a very popular frontend used to manage users and passwods for e-mail systems, written for postfix in PHP. It is accessible through a web browser.
The TLS layer, used to encrypt communications between the SMTP/POP3 client and the server. It may be used for secure message delivery between servers, if both servers support TLS.
Installation on a CentOS server should be done in the following order:
– mysql database
– dovecot
– development tools (may be installed ino a development-only machine, the tools are required to rebuild the postfix package)
– postfix. The default postfix package do not support virtual delivery agent and mysql, so it must be recompiled
– postfixadmin

Steps to Mail Server Setup

1. MySQL Database installation
2. Dovecot installation and configuration
2.1. Dovecot SSL configuration
2.2 Dovecot configuration for multiple domains
3. Postfix installation and configuration
3.1. Postfix installation from centosplus repository
3.2. Postfix compiled with dovecot SASL and virtual users support
3.3. Postfix TLS configuration
3.4. Greylisting with postgrey
4. Postfixadmin installation