Linux server admin commands

Command    Description
•    apropos whatis             Show commands pertinent to string. See also threadsafe
•    man -t man | ps2pdf – > man.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
•    nice info    Run a low priority command (The “info” reader in this case)
•    renice 19 -p $$    Make shell (script) low priority. Use for non interactive tasks
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:// 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/’~/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 $HOST
ssh -g -L 8080:localhost:80 root@$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
wget (multi purpose download tool)
•    (cd cli && wget -nd -pHEKk    Store local browsable version of a page to the current dir
wget -c    Continue downloading a partially downloaded file
wget -r -nd -np -l1 -A ‘*.jpg’    Download a set of files to the current directory
wget ftp://remote/file[1-9].iso/    FTP supports globbing directly
•    wget -q -O- | 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    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 brd + dev eth0    Add (or del) ip and mask (
•    ip route show    List routing table
ip route add default via    Set default gateway to
•    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
•    host    Lookup DNS ip address for name or vice versa
•    hostname -i    Lookup local ip address (equivalent to host `hostname`)
•    whois    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    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 ‘1000p;1000q’    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
•    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 -a1 -a2 file1 file2    Union of sorted files
join file1 file2    Intersection of sorted files
join -v2 file1 file2    Difference of sorted files
join -v1 -v2 file1 file2    Symmetric Difference of sorted files
•    echo ‘(1 + sqrt(5))/2’ | bc -l    Quick math (Calculate φ). See also bc
•    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/9.69s’ ‘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
•    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
•    [ $(date -d “tomorrow” +%d) = “01” ] || exit    exit a script unless it’s the last day of the month
•    date –date=’25 Dec’ +%A    What day does xmas fall on, this year
•    date –date=’@2147483647′    Convert seconds since the epoch (1970-01-01 UTC) to date
•    TZ=’:America/Los_Angeles’ date    What time is it on West coast of US (use tzselect to find TZ)
echo “mail -s ‘get the train’ < /dev/null” | at 17:45    Email reminder
•    echo “DISPLAY=$DISPLAY xmessage cooker” | at “NOW + 30 minutes”    Popup reminder
•    printf “%’d\n” 1234    Print number with thousands grouping appropriate to locale
•    BLOCK_SIZE=\’1 ls -l    get ls to do thousands grouping appropriate to locale
•    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 | cut -d= -f1 | xargs locale -kc | 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.txt > file.qp    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
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 *.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
•    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
•    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
•    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$COLUMNS    List processes by mem usage. See also
•    ps -C firefox-bin -L -o pid,tid,pcpu,state    List all threads for a particular process
•    ps -p 1,2    List info for particular process IDs
•    last reboot    Show system reboot history
•    free -m    Show amount of (remaining) RAM (-m displays in MB)
•    watch -n.1 ‘cat /proc/interrupts’    Watch changeable data continuously
system information (see also sysinfo) (‘#’ means root access is required)
•    uname -a    Show kernel version and system architecture
•    head -n1 /etc/issue    Show name and version of distribution
•    cat /proc/partitions    Show all partitions registered on the system
•    grep MemTotal /proc/meminfo    Show RAM total seen by the system
•    grep “model name” /proc/cpuinfo    Show CPU(s) info
•    lspci -tv    Show PCI info
•    lsusb -tv    Show USB info
•    mount | column -t    List mounted filesystems on the system (and align output)
#    dmidecode -q | less    Display SMBIOS/DMI information
#    smartctl -A /dev/sda | grep Power_On_Hours    How long has this disk (system) been powered on in total
#    hdparm -i /dev/sda    Show info about disk sda
#    hdparm -tT /dev/sda    Do a read speed test on disk sda
#    badblocks -s /dev/sda    Test for unreadable blocks on disk sda
interactive (see also linux keyboard shortcuts)
•    readline    Line editor used by bash, python, bc, gnuplot, …
•    screen    Virtual terminals with detach capability, …
•    mc    Powerful file manager that can browse rpm, tar, ftp, ssh, …
•    gnuplot    Interactive/scriptable graphing
•    links    Web browser
•    xdg-open    open a file or url with the registered desktop application
•    alias hd=’od -Ax -tx1z -v’    Handy hexdump. (usage e.g.: • hd /proc/self/cmdline | less)
•    alias realpath=’readlink -f’    Canonicalize path. (usage e.g.: • realpath ~/../$USER)
•    set | grep $USER    Search current environment
touch -c -t 0304050607 file    Set file timestamp (YYMMDDhhmm)
•    python -m SimpleHTTPServer    Serve current directory tree at http://$HOSTNAME:8000/


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