Linux Commands

A variegated collection of useful Linux commands, in no particular order

testparm smb.conf = Check the syntax of the Samba configuration file
cat /proc/interrupts = Show the IRQs
cat /proc/dma = Show the DMA channels
alignmargins = Align margins of a printer (it actually prints a test page with the margins)
import img = Take a screenshot of the desktop in img
xwd -out img = Take a screenshot of a window (to be selected with the mouse) and saves it in img in a format readable by xwud
tput reset = Reset (clean) the terminal
display 'vid:*.jpg' = Make a thumbnails gallery of all the images in the current directory
montage $images outputimg = Make a single image of all $images
zip -J file.zip /directory/files = Make a zip file of files stripping the directories tree (basically, put every file at the same level in the zip file)
lsof -V -P = Show all opened ports and the relative processes
lsof (file|device) = Show the processes using file|device
lsof -i TCP:4000 = Check if a specific port is in use
cdrecord dev=scsihost blank=fast = Blank a CDRW in fast mode. Use “all” for the complete mode
ss -s = Print statistics about the network packets
tcpdump -q = Show packets that are being transferred over the network
xwininfo = Show many informations about the selected window
uuencode file name | mail user = Encrypt the binary file as “name” and send it via e-mail to “user”
uudecode file = Decrypt a file
nmap -P -O url = Inquiry about open ports and the OS running on url
perl -MCPAN -e 'install module' = Install a Perl module
- perl -Mmodulename -e 1 = Check if “modulename” is already installed
useradd -d home -g group -G group1,group2 name = Add an user with “name”, with home directory as “home”, that belongs to group “group” and also to “group1” and “group2”
mkisofs -v -r -l --allow-leading-dots -R -J -T -o img.iso files = Make an iso file (RockRidge + Joliet)
split -B size file outputfile = Split file in as many pieces of outputfile as given size (in bytes)
rar a -v1000000k archive.rar file = Make a rar archive of at most 1000000 kilobytes from file(s)
xrdb -load .Xdefaults = Load configuration in .Xdefaults
perl -e shell -mcpan = Open a shell to manage Perl modules
- i /module/ = Search a module
- install module = Download and install a module
formail -s procmail < mbox = Scan a mbox with the current Procmail rules
setkeycodes code n = Map an unrecognized key to n so it can be bind to an atcion with xbindkeys (see logs to discover the code)
xev = Show info about the pressed key
bogoutil -p wordlist.db word = Show if word is classified as ham or spam by bogoutil
sox file.wav -v n output.wav = Raise or lower volum of a wav according to the value of n (the higher it is, the higher it’ll be the volume too)
screen -xRR = Launch screen at login. To be inserted in the shell configuration file (bashrc, zshrc etc.)
growisofs -Z /dev/hdd=image.iso = Burn the iso file in the specified device
cupsdoprint -H localhost:631 -P printername -J jobname -U login_name file.ps = Print the file.ps with the selected printer
dvdauthor -T directory = Create the TOC (the file VIDEO_TS.IFO) of a dvd in directory
dvdauthor -t dvdvideos -v videooptions -a audiooptions directory = Make the vob files from videos using the parameters for video and audio given
gtf hhhh wwww refresh_rate = Print the Modeline for xorg.conf of the given resolution (height and width) and refresh rate (in Hz)
cat /proc/fb0/modes = Show supported resolution by the current framebuffer device (fb0)
pacman -Qqe | grep -vx "$(pacman -Qqm)" = Print the list of installed packages in Archlinux (does not include those in AUR)
zcat initrd_image.img | cpio –list = Show contents of a cpio boot image
pdfimages -j file.pdf directory = Extract in ppm (Gimp can open it) all the images in file.pdf to directory. Pdfimages is in poppler package
curl -o /dev/null -s -w %{time_connect}:%{time_starttransfer}:%{time_total} url = Returns, respectively, the time needed to connect to url, the time the server took to reply and the total time taken to satisfy the request
wget -E -H -k -K -p -x webpage = Download webpage, followin images and css links and converting them to local to make browsing offline easier
wget -e robots=off --wait 1 -x -m -k url = Download url, convert link to local, wait 1 second between requests to not overload the server and ignore the robots file
udevinfo -a -p udevinfo -q path -n device = Get info on a device useful to then write an udev rule about it
ffmpeg -i video audio = Extract audio from a video. To know in what format it is, use ffmpeg -i video and look for the line that says “Stream…..Audio”
ffmpeg -i youtube.flv -ar 48000 -ac 2 -b 800000 youtube.avi = Convert in an avi a flv file, fixing audio out of sync issues. -b is the bitrate, increase it to make the final result look better (and bigger)
w = Show info about the users logged and what processes they have launched
stat file|directory = Show complete info about a file or a directory (inode number, size, occupied clusters, modification/access time etc.)
trap 'echo message' EXIT = Execute the command, in this case echoing “message”, when the script/shell receives the signal to exit (EXIT)
cat /proc/cmdline = Show kernel parameters sent at boot
nmap -sV host = Scan all open ports on host, trying to identify also the services using them
netstat -antulp host = Scan open ports and active connections on host, returning also information on the processes
cdrdao copy --on-the-fly --speed 4 --read-raw --fast-toc --device 0,1,0 --driver generic-mmc-raw --source-device 0,0,0 --source-driver generic-mmc-raw = On the fly copy of a cd (check the device numbers, of course)
cdrdao read-cd --device 6,0,0 --driver generic-mmc-raw -v 2 --datafile CD.bin --read-raw CD.toc = On the fly copy of a cd containing multisession tracks
kill -9 $(ps -o pid= -u user) = Kill all processes started by a given user, basically stopping his use of the computer
find / -xdev -type d $ -perm -0002 -a ! -perm -1000 $ -print = Find all directories that haven’t the sticky bit set and are writable by everybody (a known security hole)
find / -xdev -type f $ -perm -4000 -o -perm -2000 $ -print = Find all files with suid/sgid set
find / -xdev -type f -perm -0002 -print = Find all files that are editable by everybody
find / -xdev $ -nouser -o -nogroup $ -print = Find all files that haven’t a group or a user or have and invalid one
cat /proc/net/nf_conntrack = List all recent connections, with ports, addresses and protocols. Needs Ip Conntrack support in the kernel
modinfo module = Show detailed info about a kernel module
ls -d */ = Show only subdirectories of the current directory
lsof +p pid = Show opened files by the process with that pid
ffmpeg -f x11grab -r 25 -s 800x600 -i :0.0 /tmp/outputFile.mpg = Record a screencast of the desktop at 25fps with a 800x600 resolution
grep ^[^#] config_file = Strip and print a file of comments (#) and empty lines
grep -v '#' config_file = As above but keep empty lines
identify -format %[exif:*] img = Show Exif data of img
curl -v url = Connect to url and show request and response http headers
pacman -Qm = Show installed packages that aren’t present in the pacman database. Usually they are local and aur packages
diff -rupN original_dir/ new_dir/ > file.patch = Make a patch containing the differences in all files between original_dir and new_dir
netstat -c host = Show info about connection of host in a continuosly updated way (needs to be killed then)
curl --head -s url -D - = Connect to url with a HEAD request, outputting only the response headers
cuebreakpoints file.cue | shnsplit -o flac -t "%p-%a-%n-%t" file.flac = Split a flac file containg a full album into tracks according to the cue file. See also Archwiki entry.
cuetag.sh file.cue split-track*.flac = Add tags to the various tracks from the cue file. Usually it is to be after cuebreakpoints. See also Archwiki entry
sp-sc link 3908 8908 > /dev/null & = Connect to the Sopcast link at port 3908 and open to listen on localhost on port 8908
mplayer http://localhost:8908/tv.asf = Play the Sopcast video from above
pgrep cmd = Return the pid of cm. Like ps | grep cmd but doesn’t print also the grep pid
csplit file model = Split file in various copies named like xx00, xx01 etc. Model can be a line number or a regular expression
env -i cmd = Ignore any environment variable for the execution of cmd
ls | grep -x ".\{6\}" = Return only file or directory names whose name is long exactly 6 characters
find path -size +1000k = Find only files bigger than 1Mb in path. Using instead -1000k looks for files smaller than 1Mb and without both - and + looks for files of exactly 1Mb
fc = Open with $EDITOR the last executed command and thus enable modifying it, reexecuting it at the end
ls -t = List files ordered by modification date, the most recent first
ls -X = List files ordered by extension
ls -S = List files ordered by size, the bigger ones first
find | xargs file = List files in current directory as it was used the command file on them all
cat > file = Write text to a file without any need of a real editor. Start typing after this command and terminate input with Ctrl+d
bind -P = Show all available Bash functions and their keybindings
objdump -D prog = Disassemble prog
grep -H regexp files = Print filename of every files matching the regexp
openssl x509 -noout -fingerprint -in cert.pem = Print the SHA1 checksum of the certificate cert.pem
openssl s_client -connect server -showcerts = Show SSL info and certificates of server
openssl s_client -host server -port portnumber -verify 1 -debug = debug a secure connection with server on portnumber
nm -D cmd = Show all names, variables and functions, used by cmd
cat /proc/pid/smaps = Show loaded memory segments by the process with such pid
genisoimage -r -J -o file.iso directory = Make an iso, readable both on Windows and Linux, of the files in directory
wodim -v dev=/dev/sr0 file.iso = Burn on the empty medium in /dev/sr0 the iso
top -pnnn -pnnn = Start top telling it to monitor only processes whose pid is nnn
loginctl list-seats = Lists seats
loginctl seat-status seat0 = Shows list of hardware assigned to seat0
grep -Ri --include="*.py" abc directory/ = Search for “abc” in directory but only considering .py files
lspci -k = Print a list of active hardware devices with the corresponding kernel module they need to work
modprobe -c = Display a complete module configuration, including defaults and directives in /etc/modules.conf (or /etc/modules-load.d/, depending on the Linux distribution)
ip route show = Display routing table
ip route show table 255 = Display local addresses route table
ip route add prohibit 1.1.1.1 = Prohibit all access to the specified IP address
ip addr show = Display IP and MAC addresses of every network interface
arp = Display the ARP cache
msgcat --color=test = Output various tests to check the appearance of colours on your terminal
gcc -E file.c = See all the declarations from file.c and from all the headers included by it
date -d "string" = Emits current date and time modified by string. For example, 2 days will add 2 days to current date, 1 hour ago will subtract 1 hour, last year will emit the date exactly 1 year ago etc.
date -r file = Returns when the file was last modified
who -b = Print time and date of the last system boot
watch -n 10 kill -USR1 4834 = Print every second (0.1sec * 10) the status of the process having pid 4834
diff -rq dir1/ dir2/ = Print a summary of the differences between dir1 and dir2
cat -s file = Output only non-repeated lines from file. Like uniq
cat -a file = Output file showing tabs, non printing characters and a $ for each newline character. It’s the same as using cat -vET
stapler sel input.pdf 23-25 33 40-60 output.pdf = Create a new pdf (output.pdf) from input.pdf only including a specific range of pages (in the example, 23 through 25, the page 33 and from page 40 through 60)
bsdtar xf zipfile = Extract from a zip archive. It may work also with incomplete/corrupt ones or in general where unzip won’t.
find . -name "pattern" -ls | awk '{total += $7} END {print total}' = Print the total size of files matching pattern
curl -X POST -d "fname=Mark&lname=Babe" url = Send a POST request to url with given parameters. It’s also possible to send a JSON file containing the parameters using -d @parameters.json syntax
du -s directory/ = Show only the total sum of occupied space on disk of directory, and not every single file also
find Maildir/ -type f | grep -vE ',[^,]*S[^,]*$' = Find all unread emails in the maildir (Maildir format)
nl $file = Print the file with the lines’ numbers next to each line. By default it skips empty lines, to include them add -b a.
ip -s link show = Print all the network interfaces present on the system with additional statistics about them
ip neighbour show = Show the ARP table
route add -host $ip reject = Reject all traffic to host with IP address of $ip
ls -Z = Display SELinux context for the files
last = Display a chronological list of users’ accesses
lastb = Display a chronological list of failed users’ accesses (“bad logins”)
lastlog = Display the last accesses of each daemons and users
dig $domain +noall +answer = Display the IP address of $domain with a TTL of how long the data is kept in local DNS cache
file -i $filename = Show the mimetype and locale of $filename
ddjvu --format=pdf file.djvu file.pdf = Convert a djvu file to a pdf
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dCompressFonts=true -dDetectDuplicateImages -dPDFSETTINGS=/ebook -dNOPAUSE -dBATCH -sOUtputFile=file.pdf file_to_optimize.pdf = Compress and optimize a pdf. /ebook means a medium quality, 150dpi. Alternatives are /prepress, which produces a 300dpi pdf, and /screen, for a 72dpi, good for screen reading only, pdf. The resolution can also be forced with the option -r72 (for 72dpi).
pactl list | grep codec = Check what bluetooth codec is being used (need bluez and pavucontrol installed)
yt-dlp -S "res:720" video = Download video but only up to 720p resolution, or lower if not available
asciidoc -b docbook file.adoc = Convert an asciidoc file to a docbook XML. This is useful to then convert it later to markdown or else
- pandoc -f docbook file.xml -o file.md = Take the docbook XML file generated above and convert it to markdown