Useful Linux Commands

Command		Description
•	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
	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
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/.*