Howto enable internet for ip in Centos

#eth0 – internet
#eth1 – network
echo -e “192.168.10.99 00:15:F2:16:6C:C2 dev eth1″ > /srv/mac.list
arp -f /srv/mac.list
iptables -t nat -A POSTROUTING -o eth0-j MASQUERADE
iptables -A FORWARD -i eth1 -j ACCEPT
echo 1 > /proc/sys/net/ipv4/ip_forward
#this script enable internet for ip 192.168.10.99 with MAC 00:15:F2:16:6C:C2

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Enable IP forwarding under RHEL/CentOS

The regular way

Edit /etc/sysctl.conf

Edit the “net.ipv4.ip_forward” line and set it to 1

# Kernel sysctl configuration file for Red Hat Linux
#
# For binary values, 0 is disabled, 1 is enabled.  See sysctl(8) and
# sysctl.conf(5) for more details.

# Controls IP packet forwarding
net.ipv4.ip_forward = 1

# Controls source route verification
net.ipv4.conf.default.rp_filter = 1

# Do not accept source routing
net.ipv4.conf.default.accept_source_route = 0

# Controls the System Request debugging functionality of the kernel
kernel.sysrq = 0

# Controls whether core dumps will append the PID to the core filename.
# Useful for debugging multi-threaded applications.
kernel.core_uses_pid = 1

When done type the following to validate the new setting :

sysctl -p

The manual way :

echo "1" > /proc/sys/net/ipv4/ip_forward

This wouldn’t be persistent though, so you should edit sysctl.conf anyway, or add the command in /etc/rc.local

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Email Fundamentals: How to Send Email via Telnet

This is one of the essential troubleshooting tricks that an Exchange administrator needs to know, sending an email using Telnet from the command line.

Let’s say you’ve just configured a relay connector and want to test it from the server that you wish to allow relay from before you let that server’s owner know that it is all set up for them. Or perhaps you want to quickly test whether a another email server on the internet is accepting mail from your network.

For just about any scenario where you want to quickly test SMTP knowing this method is very useful.

Note: this technique requires the Telnet client to be installed on the computer you’re running the test from. For Windows XP and Windows Server 2003 it will already be installed, but Windows 7 and Windows Server 2008 need to install it first.

Installing the Telnet Client for Windows 7

To install the Telnet client on a Windows 7 computer use these steps.

1. Open the Control Panel
2. Click on Programs
3. Click on Turns Windows Features on or off
4. Scroll down the list until you see Telnet Client, and tick that box
5. Click OK and close the Control Panel

Installing the Telnet Client for Windows Server 2008

To install the Telnet client on a Windows Server 2008 computer open a command prompt and run the following command.

C:\>servermanagercmd -i telnet-client
.........

Start Installation...
[Installation] Succeeded: [Telnet Client].

Success: Installation succeeded.

Installing the Telnet Client for Windows Server 2008 R2

To install the Telnet client on a Windows Server 2008 R2 computer open a PowerShell window and run the following command.

PS C:\> Import-Module servermanager
PS C:\> Add-WindowsFeature telnet-client

Success Restart Needed Exit Code Feature Result
------- -------------- --------- --------------
True    No             Success   {Telnet Client}

Sending Email from the Command Line via Telnet

Open a command prompt and use Telnet to connect to the remote email server on port 25.

C:\>telnet esp-ho-ex2010a 25

If Telnet is able to connect to the remote server you should see its welcome banner.

220 ESP-HO-EX2010A.exchangeserverpro.net Microsoft ESMTP MAIL Service ready at T
ue, 9 Aug 2011 22:00:04 +1000

The first command to send is the HELO command. Some email servers will accept HELO on its own, others will require you to also provide a host or domain name along with it.

helo test.com
250 ESP-HO-EX2010A.exchangeserverpro.net Hello [10.0.1.11]

Next use the MAIL FROM command to tell the remote server who the email is from.

mail from: test@test.com
250 2.1.0 Sender OK

Now use the RCPT TO command to tell the remote server who to deliver the email to.

rcpt to: alan.reid@exchangeserverpro.net
250 2.1.5 Recipient OK

The final step for the bare minimum set of commands is the DATA command.

data
354 Start mail input; end with .

If you just want to send a blank message type a period “.” and press enter. Otherwise you can set a subject line for the message if you like. Use SUBJECT and then type your subject line, and press enter.

subject: this is a test message

Type any text you want to include with the message, press enter, and then finally type a period “.” and press enter to send the email.

sending a test message via telnet
.
250 2.6.0  [InternalId=320] Queued mail for delivery

If the message was queued for delivery then it has been accepted by the server. If this is an Exchange server that you control then you can use message tracking to troubleshoot further if the message doesn’t make it to the inbox that you were expecting.

Type the QUIT command to terminate the connection when you’re done.

SMTP Status Codes

You may notice along the way that after typing commands you see responses from the server starting with “250″.

250 is a good thing, and there are a lot of other SMTP status codes you’ll encounter the more you use this technique. For example an email server may deny your attempt to relay mail between two domains.

550 5.7.1 Unable to relay

Or you may encounter an email server that is explicitly blocking email from your domain.

554 5.1.0 Sender denied

There are a lot of different scenarios you might encounter here, and thankfully the SMTP status codes will help you troubleshoot them.

Now that you understand how to send email using Telnet and the command line I hope you find this technique very useful in the future.

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Set Multiple Sites as a Homepage in Internet Explorer 9

The Procedure for Setting the Homepage

First, open Internet Explorer 9 and then a tab for each site you want to set as a homepage. Browse to those websites.

Once you have all the websites loaded, click on the Tools button from the upper-right side of the Internet Explorer window. Then, click on Internet Options.

You set the homepage in the General tab. Simply click ’Use current’.

The websites you have loaded in each tab are now set as a homepage.Click OKand you are done.

From now on, when you start Internet Explorer 9, the websites which you set as homepages will be loaded in separate tabs.

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Enabling And Disabling Services During Start Up In GNU/Linux

In any Linux distribution, some services are enabled to start at boot up by default. For example, on my machine, I have pcmcia, cron daemon, postfix mail transport agent ... just to name a few, which start during boot up. Usually, it is prudent to disable all services that are not needed as they are potential security risks and also they unnecessarily waste hardware resources. For example, my machine does not have any pcmcia cards so I can safely disable it. Same is the case with postfix which is also not used.

So how do you disable these services so that they are not started at boot time?

The answer to that depends on the type of Linux distribution you are using. True, many Linux distributions including Ubuntu bundle with them a GUI front end to accomplish the task which makes it easier to enable and disable the system services. But there is no standard GUI utility common across all Linux distributions. And this makes it worth while to learn how to enable and disable the services via the command line.

But one thing is common for all Linux distributions which is that all the start-up scripts are stored in the '/etc/init.d/' directory. So if you want to say, enable apache webserver in different run levels, then you should have a script related to the apache webserver in the /etc/init.d/ directory. It is usually created at the time of installing the software. And in my machine (which runs Ubuntu), it is named apache2. Where as in Red Hat, it is named httpd. Usually, the script will have the same name as the process or daemon.

Here I will explain different ways of enabling and disabling the system services.
1) Red Hat Method

Red Hat and Red Hat based Linux distributions make use of the script called chkconfig to enable and disable the system services running in Linux.

For example, to enable the apache webserver to start in certain run levels, you use the chkconfig script to enable it in the desired run levels as follows:

# chkconfig httpd --add
# chkconfig  httpd  on --level 2,3,5

This will enable the apache webserver to automatically start in the run levels 2, 3 and 5. You can check this by running the command:

# chkconfig --list httpd

One can also disable the service by using the off flag as shown below:

# chkconfig httpd off
# chkconfig httpd --del

Red Hat also has a useful script called service which can be used to start or stop any service. Taking the previous example, to start apache webserver, you execute the command:

# service httpd start

and to stop the service...

# service httpd stop

The options being start, stop and restart which are self explanatory.
2) Debian Method

Debian Linux has its own script to enable and disable services across runlevels. It is called update-rc.d. Going by the above example, you can enable apache webserver as follows:

# update-rc.d apache2 defaults

... this will enable the apache webserver to start in the default run levels of 2,3,4 and 5. Of course, you can do it explicitly by giving the run levels instead of the "defaults" keyword as follows:

# update-rc.d apache2 start 20 2 3 4 5 . stop 80 0 1 6 .

The above command modifies the sym-links in the respective /etc/rcX.d directories to start or stop the service in the destined runlevels. Here X stands for a value of 0 to 6 depending on the runlevel. One thing to note here is the dot (.) which is used to terminate the set which is important. Also 20 and 80 are the sequence codes which decides in what order of precedence the scripts in the /etc/init.d/ directory should be started or stopped.

And to disable the service in all the run levels, you execute the command:

# update-rc.d -f apache2 remove

Here -f option which stands for force is mandatory.

But if you want to enable the service only in runlevel 5, you do this instead:

# update-rc.d apache2  start 20 5 . stop 80 0 1 2 3 4 6 .

3) Gentoo Method

Gentoo also uses a script to enable or disable services during boot-up. The name of the script is rc-update . Gentoo has three default runlevels. Them being: boot, default and nonetwork. Suppose I want to add the apache webserver to start in the default runlevel, then I run the command:

# rc-update add apache2 default

... and to remove the webserver, it is as simple as :

# rc-update del apache2

To see all the running applications at your runlevel and their status, similar to what is achieved by chkconfig --list, you use the rc-status command.

# rc-status --all

4) The old fashioned way

I remember the first time I started using Linux, there were no such scripts to aid the user in enabling or disabling the services during start-up. You did it the old fashioned way which was creating or deleting symbolic links in the respective /etc/rcX.d/ directories. Here X in rcX.d is a number which stands for the runlevel. There can be two kinds of symbolic links in the /etc/rcX.d/ directories. One starts with the character 'S' followed by a number between 0 and 99 to denote the priority, followed by the name of the service you want to enable. The second kind of symlink has a name which starts with a 'K' followed by a number and then the name of the service you want to disable. So in any runlevel, at any given time, for each service, there should be only one symlink of the 'S' or 'K' variety but not both.

So taking the above example, suppose I want to enable apache webserver in the runlevel 5 but want to disable it in all other runlevels, I do the following:

First to enable the service for run level 5, I move into /etc/rc5.d/ directory and create a symlink to the apache service script residing in the /etc/init.d/ directory as follows:

# cd /etc/rc5.d/
# ln -s /etc/init.d/apache2 S20apache2

This creates a symbolic link in the /etc/rc5.d/ directory which the system interprets as - start (S) the apache service before all the services which have a priority number greater than 20.

If you do a long listing of the directory /etc/rc5.d in your system, you can find a lot of symlinks similar to the one below.

lrwxrwxrwx  1 root root 17 Mar 31 13:02 S20apache2 -> ../init.d/apache2

Now if I start a service, I will want to stop the service while rebooting or while moving to single user mode and so on. So in those run levels I have to create the symlinks starting with character 'K'. So going back to the apache2 service example, if I want to automatically stop the service when the system goes into runlevel 0, 1 or 6, I will have to create the symlinks as follows in the /etc/rc0.d, /etc/rc1.d/, /etc/rc6.d/ directories.

# ln -s /etc/init.d/apache2 K80apache2

One interesting aspect here is the priority. Lower the number, the higher is the priority. So since the starting priority of apache2 is 20 - that is apache starts way ahead of other services during startup, we give it a stopping priority of 80. There is no hard and fast rule for this but usually, you follow the formula as follows:

If you have 'N' as the priority number for starting a service, you use the number (100-N) for the stopping priority number and vice versa.

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Basic vi Commands

Linux
i or insert to insert text
ii ir insert insert to replace (overwrite)
arrow keys to navigate
esc :q! to exit with out changes
esc :wq to save and exit
my fave
esc shift^ZZ to save and exit.

*BSD
same as above but no arrow keys and sometimes no insert i(only)
esc takes you to command mode and you can navigate
.with keys
x =delete
h,j,k,l = arrows
etc...
just the very basics
Almost forgot that *BSD has an editor ee I like alot when you're done editing
esc and you get a little menu

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linux command line reference for common operations

 

 

This is a linux command line reference for common operations.
Examples marked with • are valid/safe to paste without modification into a terminal, so
you may want to keep a terminal window open while reading this so you can cut & paste.
All these commands have been tested both on Fedora and Ubuntu.

 

 

Command		Description
•	apropos whatis	Show commands pertinent to string. See also threadsafe
•	man -t ascii | ps2pdf - > ascii.pdf	make a pdf of a manual page
	which command	Show full path name of command
	time command	See how long a command takes
•	time cat	Start stopwatch. Ctrl-d to stop. See also sw
dir navigation
•	cd -	Go to previous directory
•	cd	Go to $HOME directory
	(cd dir && command)	Go to dir, execute command and return to current dir
•	pushd .	Put current dir on stack so you can popd back to it
file searching
•	alias l='ls -l --color=auto'	quick dir listing
•	ls -lrt	List files by date. See also newest and find_mm_yyyy
•	ls /usr/bin | pr -T9 -W$COLUMNS	Print in 9 columns to width of terminal
	find -name '*.[ch]' | xargs grep -E 'expr'	Search 'expr' in this dir and below. See also findrepo
	find -type f -print0 | xargs -r0 grep -F 'example'	Search all regular files for 'example' in this dir and below
	find -maxdepth 1 -type f | xargs grep -F 'example'	Search all regular files for 'example' in this dir
	find -maxdepth 1 -type d | while read dir; do echo $dir; echo cmd2; done	Process each item with multiple commands (in while loop)
•	find -type f ! -perm -444	Find files not readable by all (useful for web site)
•	find -type d ! -perm -111	Find dirs not accessible by all (useful for web site)
•	locate -r 'file[^/]*\.txt'	Search cached index for names. This re is like glob *file*.txt
•	look reference	Quickly search (sorted) dictionary for prefix
•	grep --color reference /usr/share/dict/words	Highlight occurances of regular expression in dictionary
archives and compression
	gpg -c file	Encrypt file
	gpg file.gpg	Decrypt file
	tar -c dir/ | bzip2 > dir.tar.bz2	Make compressed archive of dir/
	bzip2 -dc dir.tar.bz2 | tar -x	Extract archive (use gzip instead of bzip2 for tar.gz files)
	tar -c dir/ | gzip | gpg -c | ssh user@remote 'dd of=dir.tar.gz.gpg'	Make encrypted archive of dir/ on remote machine
	find dir/ -name '*.txt' | tar -c --files-from=- | bzip2 > dir_txt.tar.bz2	Make archive of subset of dir/ and below
	find dir/ -name '*.txt' | xargs cp -a --target-directory=dir_txt/ --parents	Make copy of subset of dir/ and below
	( tar -c /dir/to/copy ) | ( cd /where/to/ && tar -x -p )	Copy (with permissions) copy/ dir to /where/to/ dir
	( cd /dir/to/copy && tar -c . ) | ( cd /where/to/ && tar -x -p )	Copy (with permissions) contents of copy/ dir to /where/to/
	( tar -c /dir/to/copy ) | ssh -C user@remote 'cd /where/to/ && tar -x -p'	Copy (with permissions) copy/ dir to remote:/where/to/ dir
	dd bs=1M if=/dev/sda | gzip | ssh user@remote 'dd of=sda.gz'	Backup harddisk to remote machine
rsync (Network efficient file copier: Use the --dry-run option for testing)
	rsync -P rsync://rsync.server.com/path/to/file file	Only get diffs. Do multiple times for troublesome downloads
	rsync --bwlimit=1000 fromfile tofile	Locally copy with rate limit. It's like nice for I/O
	rsync -az -e ssh --delete ~/public_html/ remote.com:'~/public_html'	Mirror web site (using compression and encryption)
	rsync -auz -e ssh remote:/dir/ . && rsync -auz -e ssh . remote:/dir/	Synchronize current directory with remote one
ssh (Secure SHell)
	ssh $USER@$HOST command	Run command on $HOST as $USER (default command=shell)
•	ssh -f -Y $USER@$HOSTNAME xeyes	Run GUI command on $HOSTNAME as $USER
	scp -p -r $USER@$HOST: file dir/	Copy with permissions to $USER's home directory on $HOST
	scp -c arcfour $USER@$LANHOST: bigfile	Use faster crypto for local LAN. This might saturate GigE
	ssh -g -L 8080:localhost:80 root@$HOST	Forward connections to $HOSTNAME:8080 out to $HOST:80
	ssh -R 1434:imap:143 root@$HOST	Forward connections from $HOST:1434 in to imap:143
	ssh-copy-id $USER@$HOST	Install public key for $USER@$HOST for password-less log in
wget (multi purpose download tool)
•	(cd dir/ && wget -nd -pHEKk http://www.pixelbeat.org/cmdline.html)	Store local browsable version of a page to the current dir
	wget -c http://www.example.com/large.file	Continue downloading a partially downloaded file
	wget -r -nd -np -l1 -A '*.jpg' http://www.example.com/dir/	Download a set of files to the current directory
	wget ftp://remote/file[1-9].iso/	FTP supports globbing directly
•	wget -q -O- http://www.pixelbeat.org/timeline.html | grep 'a href' | head	Process output directly
	echo 'wget url' | at 01:00	Download url at 1AM to current dir
	wget --limit-rate=20k url	Do a low priority download (limit to 20KB/s in this case)
	wget -nv --spider --force-html -i bookmarks.html	Check links in a file
	wget --mirror http://www.example.com/	Efficiently update a local copy of a site (handy from cron)
networking (Note ifconfig, route, mii-tool, nslookup commands are obsolete)
	ethtool eth0	Show status of ethernet interface eth0
	ethtool --change eth0 autoneg off speed 100 duplex full	Manually set ethernet interface speed
	iwconfig eth1	Show status of wireless interface eth1
	iwconfig eth1 rate 1Mb/s fixed	Manually set wireless interface speed
•	iwlist scan	List wireless networks in range
•	ip link show	List network interfaces
	ip link set dev eth0 name wan	Rename interface eth0 to wan
	ip link set dev eth0 up	Bring interface eth0 up (or down)
•	ip addr show	List addresses for interfaces
	ip addr add 1.2.3.4/24 brd + dev eth0	Add (or del) ip and mask (255.255.255.0)
•	ip route show	List routing table
	ip route add default via 1.2.3.254	Set default gateway to 1.2.3.254
•	host pixelbeat.org	Lookup DNS ip address for name or vice versa
•	hostname -i	Lookup local ip address (equivalent to host `hostname`)
•	whois pixelbeat.org	Lookup whois info for hostname or ip address
•	netstat -tupl	List internet services on a system
•	netstat -tup	List active connections to/from system
windows networking (Note samba is the package that provides all this windows specific networking support)
•	smbtree	Find windows machines. See also findsmb
	nmblookup -A 1.2.3.4	Find the windows (netbios) name associated with ip address
	smbclient -L windows_box	List shares on windows machine or samba server
	mount -t smbfs -o fmask=666,guest //windows_box/share /mnt/share	Mount a windows share
	echo 'message' | smbclient -M windows_box	Send popup to windows machine (off by default in XP sp2)
text manipulation (Note sed uses stdin and stdout. Newer versions support inplace editing with the -i option)
	sed 's/string1/string2/g'	Replace string1 with string2
	sed 's/\(.*\)1/\12/g'	Modify anystring1 to anystring2
	sed '/ *#/d; /^ *$/d'	Remove comments and blank lines
	sed ':a; /\\$/N; s/\\\n//; ta'	Concatenate lines with trailing \
	sed 's/[ \t]*$//'	Remove trailing spaces from lines
	sed 's/\([`"$\]\)/\\\1/g'	Escape shell metacharacters active within double quotes
•	seq 10 | sed "s/^/      /; s/ *\(.\{7,\}\)/\1/"	Right align numbers
	sed -n '1000{p;q}'	Print 1000th line
	sed -n '10,20p;20q'	Print lines 10 to 20
	sed -n 's/.*<title>\(.*\)<\/title>.*/\1/ip;T;q'	Extract title from HTML web page
	sed -i 42d ~/.ssh/known_hosts	Delete a particular line
	sort -t. -k1,1n -k2,2n -k3,3n -k4,4n	Sort IPV4 ip addresses
•	echo 'Test' | tr '[:lower:]' '[:upper:]'	Case conversion
•	tr -dc '[:print:]' < /dev/urandom	Filter non printable characters
•	tr -s '[:blank:]' '\t' </proc/diskstats | cut -f4	cut fields separated by blanks
•	history | wc -l	Count lines
set operations (Note you can export LANG=C for speed. Also these assume no duplicate lines within a file)
	sort file1 file2 | uniq	Union of unsorted files
	sort file1 file2 | uniq -d	Intersection of unsorted files
	sort file1 file1 file2 | uniq -u	Difference of unsorted files
	sort file1 file2 | uniq -u	Symmetric Difference of unsorted files
	join -t'\0' -a1 -a2 file1 file2	Union of sorted files
	join -t'\0' file1 file2	Intersection of sorted files
	join -t'\0' -v2 file1 file2	Difference of sorted files
	join -t'\0' -v1 -v2 file1 file2	Symmetric Difference of sorted files
math
•	echo '(1 + sqrt(5))/2' | bc -l	Quick math (Calculate φ). See also bc
•	seq -f '4/%g' 1 2 99999 | paste -sd-+ | bc -l	Calculate π the unix way
•	echo 'pad=20; min=64; (100*10^6)/((pad+min)*8)' | bc	More complex (int) e.g. This shows max FastE packet rate
•	echo 'pad=20; min=64; print (100E6)/((pad+min)*8)' | python	Python handles scientific notation
•	echo 'pad=20; plot [64:1518] (100*10**6)/((pad+x)*8)' | gnuplot -persist	Plot FastE packet rate vs packet size
•	echo 'obase=16; ibase=10; 64206' | bc	Base conversion (decimal to hexadecimal)
•	echo $((0x2dec))	Base conversion (hex to dec) ((shell arithmetic expansion))
•	units -t '100m/9.58s' 'miles/hour'	Unit conversion (metric to imperial)
•	units -t '500GB' 'GiB'	Unit conversion (SI to IEC prefixes)
•	units -t '1 googol'	Definition lookup
•	seq 100 | (tr '\n' +; echo 0) | bc	Add a column of numbers. See also add and funcpy
calendar
•	cal -3	Display a calendar
•	cal 9 1752	Display a calendar for a particular month year
•	date -d fri	What date is it this friday. See also day
•	[ $(date -d "tomorrow" +%d) = "01" ] || exit	exit a script unless it's the last day of the month
•	date --date='25 Dec' +%A	What day does xmas fall on, this year
•	date --date='@2147483647'	Convert seconds since the epoch (1970-01-01 UTC) to date
•	TZ='America/Los_Angeles' date	What time is it on west coast of US (use tzselect to find TZ)
•	date --date='TZ="America/Los_Angeles" 09:00 next Fri'	What's the local time for 9AM next Friday on west coast US
locales
•	printf "%'d\n" 1234	Print number with thousands grouping appropriate to locale
•	BLOCK_SIZE=\'1 ls -l	Use locale thousands grouping in ls. See also l
•	echo "I live in `locale territory`"	Extract info from locale database
•	LANG=en_IE.utf8 locale int_prefix	Lookup locale info for specific country. See also ccodes
•	locale -kc $(locale | sed -n 's/\(LC_.\{4,\}\)=.*/\1/p') | less	List fields available in locale database
recode (Obsoletes iconv, dos2unix, unix2dos)
•	recode -l | less	Show available conversions (aliases on each line)
	recode windows-1252.. file_to_change.txt	Windows "ansi" to local charset (auto does CRLF conversion)
	recode utf-8/CRLF.. file_to_change.txt	Windows utf8 to local charset
	recode iso-8859-15..utf8 file_to_change.txt	Latin9 (western europe) to utf8
	recode ../b64 < file.txt > file.b64	Base64 encode
	recode /qp.. < file.qp > file.txt	Quoted printable decode
	recode ..HTML < file.txt > file.html	Text to HTML
•	recode -lf windows-1252 | grep euro	Lookup table of characters
•	echo -n 0x80 | recode latin-9/x1..dump	Show what a code represents in latin-9 charmap
•	echo -n 0x20AC | recode ucs-2/x2..latin-9/x	Show latin-9 encoding
•	echo -n 0x20AC | recode ucs-2/x2..utf-8/x	Show utf-8 encoding
CDs
	gzip < /dev/cdrom > cdrom.iso.gz	Save copy of data cdrom
	mkisofs -V LABEL -r dir | gzip > cdrom.iso.gz	Create cdrom image from contents of dir
	mount -o loop cdrom.iso /mnt/dir	Mount the cdrom image at /mnt/dir (read only)
	cdrecord -v dev=/dev/cdrom blank=fast	Clear a CDRW
	gzip -dc cdrom.iso.gz | cdrecord -v dev=/dev/cdrom -	Burn cdrom image (use dev=ATAPI -scanbus to confirm dev)
	cdparanoia -B	Rip audio tracks from CD to wav files in current dir
	cdrecord -v dev=/dev/cdrom -audio -pad *.wav	Make audio CD from all wavs in current dir (see also cdrdao)
	oggenc --tracknum='track' track.cdda.wav -o 'track.ogg'	Make ogg file from wav file
disk space (See also FSlint)
•	ls -lSr	Show files by size, biggest last
•	du -s * | sort -k1,1rn | head	Show top disk users in current dir. See also dutop
•	du -hs /home/* | sort -k1,1h	Sort paths by easy to interpret disk usage
•	df -h	Show free space on mounted filesystems
•	df -i	Show free inodes on mounted filesystems
•	fdisk -l	Show disks partitions sizes and types (run as root)
•	rpm -q -a --qf '%10{SIZE}\t%{NAME}\n' | sort -k1,1n	List all packages by installed size (Bytes) on rpm distros
•	dpkg-query -W -f='${Installed-Size;10}\t${Package}\n' | sort -k1,1n	List all packages by installed size (KBytes) on deb distros
•	dd bs=1 seek=2TB if=/dev/null of=ext3.test	Create a large test file (taking no space). See also truncate
•	> file	truncate data of file or create an empty file
monitoring/debugging
•	tail -f /var/log/messages	Monitor messages in a log file
•	strace -c ls >/dev/null	Summarise/profile system calls made by command
•	strace -f -e open ls >/dev/null	List system calls made by command
•	strace -f -e trace=write -e write=1,2 ls >/dev/null	Monitor what's written to stdout and stderr
•	ltrace -f -e getenv ls >/dev/null	List library calls made by command
•	lsof -p $$	List paths that process id has open
•	lsof ~	List processes that have specified path open
•	tcpdump not port 22	Show network traffic except ssh. See also tcpdump_not_me
•	ps -e -o pid,args --forest	List processes in a hierarchy
•	ps -e -o pcpu,cpu,nice,state,cputime,args --sort pcpu | sed '/^ 0.0 /d'	List processes by % cpu usage
•	ps -e -orss=,args= | sort -b -k1,1n | pr -TW$COLUMNS	List processes by mem (KB) usage. See also ps_mem.py
•	ps -C firefox-bin -L -o pid,tid,pcpu,state	List all threads for a particular process
•	ps -p 1,$$ -o etime=	List elapsed wall time for particular process IDs
•	last reboot	Show system reboot history
•	free -m	Show amount of (remaining) RAM (-m displays in MB)
•	watch -n.1 'cat /proc/interrupts'	Watch changeable data continuously
•	udevadm monitor	Monitor udev events to help configure rules
system information (see also sysinfo) ('#' means root access is required)
•	uname -a	Show kernel version and system architecture
•	head -n1 /etc/issue	Show name and version of distribution
•	cat /proc/partitions	Show all partitions registered on the system
•	grep MemTotal /proc/meminfo	Show RAM total seen by the system
•	grep "model name" /proc/cpuinfo	Show CPU(s) info
•	lspci -tv	Show PCI info
•	lsusb -tv	Show USB info
•	mount | column -t	List mounted filesystems on the system (and align output)
•	grep -F capacity: /proc/acpi/battery/BAT0/info	Show state of cells in laptop battery
#	dmidecode -q | less	Display SMBIOS/DMI information
#	smartctl -A /dev/sda | grep Power_On_Hours	How long has this disk (system) been powered on in total
#	hdparm -i /dev/sda	Show info about disk sda
#	hdparm -tT /dev/sda	Do a read speed test on disk sda
#	badblocks -s /dev/sda	Test for unreadable blocks on disk sda
interactive (see also linux keyboard shortcuts)
•	readline	Line editor used by bash, python, bc, gnuplot, ...
•	screen	Virtual terminals with detach capability, ...
•	mc	Powerful file manager that can browse rpm, tar, ftp, ssh, ...
•	gnuplot	Interactive/scriptable graphing
•	links	Web browser
•	xdg-open .	open a file or url with the registered desktop application

Command		Description
•	grep . /proc/sys/net/ipv4/*	List the contents of flag files
•	set | grep $USER	Search current environment
•	tr '\0' '\n' < /proc/$$/environ	Display the startup environment for any process
•	echo $PATH | tr : '\n'	Display the $PATH one per line
•	kill -0 $$ && echo process exists and can accept signals	Check for the existence of a process (pid)
•	find /etc -readable | xargs less -K -p'*ntp' -j $((${LINES:-25}/2))	Search paths and data with full context. Use n to iterate
Low impact admin
#	apt-get install "package" -o Acquire::http::Dl-Limit=42 \ -o Acquire::Queue-mode=access	Rate limit apt-get to 42KB/s
	echo 'wget url' | at 01:00	Download url at 1AM to current dir
#	apache2ctl configtest && apache2ctl graceful	Restart apache if config is OK
•	nice openssl speed sha1	Run a low priority command (openssl benchmark)
•	renice 19 -p $$; ionice -c3 -p $$	Make shell (script) low priority. Use for non interactive tasks
Interactive monitoring
•	watch -t -n1 uptime	Clock with system load
•	htop -d 5	Better top (scrollable, tree view, lsof/strace integration, ...)
•	iotop	What's doing I/O
#	watch -d -n30 "nice ps_mem.py | tail -n $((${LINES:-12}-2))"	What's using RAM
#	iftop	What's using the network. See also iptraf
#	mtr www.pixelbeat.org	ping and traceroute combined
Useful utilities
•	pv < /dev/zero > /dev/null	Progress Viewer for data copying from files and pipes
•	wkhtml2pdf http://.../linux_commands.html linux_commands.pdf	Make a pdf of a web page
•	timeout 1 sleep 3	run a command with bounded time. See also timeout
Networking
•	python -m SimpleHTTPServer	Serve current directory tree at http://$HOSTNAME:8000/
•	openssl s_client -connect www.google.com:443 </dev/null 2>&0 | openssl x509 -dates -noout	Display the date range for a site's certs
•	curl -I www.pixelbeat.org	Display the server headers for a web site
#	lsof -i tcp:80	What's using port 80
#	httpd -S	Display a list of apache virtual hosts
•	vim scp://user@remote//path/to/file	Edit remote file using local vim. Good for high latency links
•	curl -s http://www.pixelbeat.org/pixelbeat.asc | gpg --import	Import a gpg key from the web
•	tc qdisc add dev lo root handle 1:0 netem delay 20msec	Add 20ms latency to loopback device (for testing)
•	tc qdisc del dev lo root	Remove latency added above
Notification
•	echo "DISPLAY=$DISPLAY xmessage cooker" | at "NOW +30min"	Popup reminder
•	notify-send "subject" "message"	Display a gnome popup notification
	echo "mail -s 'go home' P@draigBrady.com < /dev/null" | at 17:30	Email reminder
	uuencode file name | mail -s subject P@draigBrady.com	Send a file via email
	ansi2html.sh | mail -a "Content-Type: text/html" P@draigBrady.com	Send/Generate HTML email
Better default settings (useful in your .bashrc)
#	tail -s.1 -f /var/log/messages	Display file additions more responsively
•	seq 100 | tail -n $((${LINES:-12}-2))	Display as many lines as possible without scrolling
#	tcpdump -s0	Capture full network packets
Useful functions/aliases (useful in your .bashrc)
•	md () { mkdir -p "$1" && cd "$1"; }	Change to a new directory
•	strerror() { python -c "import os; print os.strerror($1)"; }	Display the meaning of an errno
•	plot() { { echo 'plot "-"' "$@"; cat; } | gnuplot -persist; }	Plot stdin. (e.g: • seq 1000 | sed 's/.*/s(&)/' | bc -l | plot)
•	hili() { e="$1"; shift; grep --col=always -Eih "$e|$" "$@"; }	highlight occurences of expr. (e.g: • env | hili $USER)
•	alias hd='od -Ax -tx1z -v'	Hexdump. (usage e.g.: • hd /proc/self/cmdline | less)
•	alias realpath='readlink -f'	Canonicalize path. (usage e.g.: • realpath ~/../$USER)
Multimedia
•	DISPLAY=:0.0 import -window root orig.png	Take a (remote) screenshot
•	convert -filter catrom -resize '600x>' orig.png 600px_wide.png	Shrink to width, computer gen images or screenshots
	mplayer -ao pcm -vo null -vc dummy /tmp/Flash*	Extract audio from flash video to audiodump.wav
	ffmpeg -i filename.avi	Display info about multimedia file
•	ffmpeg -f x11grab -s xga -r 25 -i :0 -sameq demo.mpg	Capture video of an X display
DVD
	for i in $(seq 9); do ffmpeg -i $i.avi -target pal-dvd $i.mpg; done	Convert video to the correct encoding and aspect for DVD
	dvdauthor -odvd -t -v "pal,4:3,720xfull" *.mpg;dvdauthor -odvd -T	Build DVD file system. Use 16:9 for widescreen input
	growisofs -dvd-compat -Z /dev/dvd -dvd-video dvd	Burn DVD file system to disc
Unicode
•	python -c "import unicodedata as u; print u.name(unichr(0x2028))"	Lookup a unicode character
•	uconv -f utf8 -t utf8 -x nfc	Normalize combining characters
•	printf '\300\200' | iconv -futf8 -tutf8 >/dev/null	Validate UTF-8
•	printf 'ŨTF8\n' | LANG=C grep --color=always '[^ -~]\+'	Highlight non printable ASCII chars in UTF-8
•	fc-match -s "sans:lang=zh"	List font match order for language and style
Development
•	gcc -march=native -E -v -</dev/null 2>&1|sed -n 's/.*-mar/-mar/p'	Show autodetected gcc tuning params. See also gcccpuopt
•	for i in $(seq 4); do { [ $i = 1 ] && wget http://url.ie/6lko -qO-|| ./a.out; } | tee /dev/tty | gcc -xc - 2>/dev/null; done	Compile and execute C code from stdin
•	cpp -dM /dev/null	Show all predefined macros
•	echo "#include <features.h>" | cpp -dN | grep "#define __USE_"	Show all glibc feature macros
	gdb -tui	Debug showing source code context in separate windows
Extended Attributes (Note you may need to (re)mount with "acl" or "user_xattr" options)
•	getfacl .	Show ACLs for file
•	setfacl -m u:nobody:r .	Allow a specific user to read file
•	setfacl -x u:nobody .	Delete a specific user's rights to file
	setfacl --default -m group:users:rw- dir/	Set umask for a for a specific dir
	getcap file	Show capabilities for a program
	setcap cap_net_raw+ep your_gtk_prog	Allow gtk program raw access to network
•	stat -c%C .	Show SELinux context for file
	chcon ... file	Set SELinux context for file (see also restorecon)
•	getfattr -m- -d .	Show all extended attributes (includes selinux,acls,...)
•	setfattr -n "user.foo" -v "bar" .	Set arbitrary user attributes
BASH specific
•	echo 123 | tee >(tr 1 a) | tr 1 b	Split data to 2 commands (using process substitution)
	meld local_file <(ssh host cat remote_file)	Compare a local and remote file (using process substitution)
Multicore
•	taskset -c 0 nproc	Restrict a command to certain processors
•	find -type f -print0 | xargs -r0 -P$(nproc) -n10 md5sum	Process files in parallel over available processors
	sort -m <(sort data1) <(sort data2) >data.sorted	Sort separate data files over 2 processors

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