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Linux tips and tricks

Posted on December 01, 2015 in computer-science

I always welcome suggestions to add new tips, to correct or improve existing ones.

Unless otherwise indicated, the tips assume that you are using the bash shell.

For an introduction to the shell, I recommend Learning the shell and the book The Linux command line by the same author (William Shotts)[^1].

Get information about your system

To check how many CPU/cores are available on your machine:

lscpu

To check the total amount of RAM installed on your computer and how much is currently being used by Linux:

free -h

To display the version of the linux kernel

uname -a

Check the performance of your comXMODIFIERS=emacsputer

You can monitor your system with glances:

glances -t 5

or with htop:

htop -d 50 --sort-key PERCENT_CPU
htop -d 50 --sort-key M_RESIDENT

There are more specialized tools that focus on subsystems. For example, you can monitor the global activity of the CPUs with:

mpstat 5

To monitor the memory usage in real-time:

vmstat -S M 10

If any of the indicators si (swap in) or so (swap out) are high, your computer lacks memory and is using the swap (memory on disk).

You can check the file input/ouput volume and speed on the local drives:

iostat -x 2 5
iostat -h -d 10

Check the speed of your ethernet connection. Three tools are available:

mii-tool

ethtool

iperf

Or the general network performance:

netstat -i 10

Large TX-ERR or RX-ERR indicate a problem.

To check the temperatures:

sudo apt install lm-sensors hddtemp
sudo sensors-detect
sensors

You can then to install psensor to continously monitor:

sudo apt install psensor

List the programs currently running on the system

To list all the processes currently running:

ps -ef

(you may omit the 'a' option if you want to list only the processes owned by you, and -l if you want less information)

The most important columns are 'time' and 'RSS' which show the time used by process since it started and the amount of real memory it takes.

If you want to list just some programs, for example `matlab``, type

pgrep -a matlab

Sometimes, it can useful to find the process that own an open file:

lsof

(See http://www.thegeekstuff.com/2012/08/lsof-command-examples/)

Kill a program that is no longer responsive

It may happen that a program monopolizes most of the CPU, but does not longer respond to input. Such a program is crashed and should be "killed"".

For applications running in a terminal, first try to press Ctrl-C.

If this does not work, or if the application is running in its own window but refusing to close, open a terminal and type:

pkill program_name

You can also use the command ps -ef to locate the application and note down the "process identification number" in the 'PID' column. Then, type:

kill PID

(in place of PID, use the number associated to the process listed in 'ps' output). Check if the program was destroyed with the ps command; if not:

kill -9 PID

If the whole graphics system no longer responds, you can try to open a text mode terminal with Ctrl-Alt-F1 or Ctrl-Alt-F2, log in and kill the programs that causes problem. Sometimes, the only solution is to kill Xorg, the display server). display).

It the keyboard does not repond anymore, before switching off the computer, you can try to connect from another computer on the same network and kill the applications or do a proper shutdown (typing 'halt' on the command line).

Printing

To get a list of available printers:

lpstat -p -d

To check the status of all printers:

lpstat -a

To put the 'file.ps' in the printing queue of the printer 'printername':

lpr -P printername file.ps

To print two copies of a file

lpr -# 2 filename

To print 2 pages per side:

lpr -o number-up=2 -o sides=two-sides-looxford university pressng-edge filename

To remove a printing job:

lprm job-id

(job-id is the number reported by the lpr or lpstat commands).

If your system uses the 'CUPS' printing system , you can control it by opening the following address in a browser:

http://local host:631/

Check out https://developer.ibm.com/tutorials/l-lpic1-108-4/ for more information.

Check the space left on disks

To see the space available on the mounted partitions:

df -h

If there is a quota system that limits the amount of space you can use on your account, you can check how much:

quota -s

Check the amount of disk space occupied by files or directories

To list the files in the current directory sorted by size:

ls -Sl

To display the size occupied by a directory:

du -h dirname

To find the largest sub-directories:

du -k | sort -rn

The following tools are quite handy to detect large files and clean one's hardrive

ncdu     # interactive du with ncurses interface 
baobab   # gui du

Find duplicate files

The command fdupes finds duplicate files and list them.

fdupes -r

A more powerful tool, fslint-gui, can detect :

  • Duplicate files
  • Problematic filenames
  • Temporary files
  • Bad symlinks
  • Empty directories
  • Nonstripped binaries

    python2 /usr/bin/fslint-gui

Find files or directories

To locate the file named 'filename' in all the subdirectories of the current directory:

find -iname 'filename'

You can use a pattern in place of 'filename', e.g. to return the list of all .doc files in the current directory and its subdirectories:

find -iname '*.doc'

You can limit the depth of subdirectoies visited:

find -maxdepth 2 -name '*.doc'

You can specify a time range:

find -mtime 0  # find the files created or modified in the last 24hours
find -mtime +30 -mtime -60  # find files modified in the last 30-60 days
find -newermt 20171101 ! -newermt 20171201 -name '*.pdf' -ls  # find pdf files modified between two dates

You can specify that you only search for, e.g., directories, using the -type argument:

find -type d # list all subdirectorectries
find -type d -mtime -10  # find the directories created or modified in the last 10 days:

You can find and delete all empty directories:

find . -type d -empty -print
find . -type d -empty -delete

You can filter on permissions

find -perm -o+x -ls -type f  # list all file with the execute flag on 'others'

You can also execute a command on each file:

find -name '*~' -exec rm '{}' '+'  # delete all files '*~'
find -name '*.py' -exec mv -t path '{}' '+'  # move all py files to path
find -name '*.txt' -print0 | xargs -0 grep -l Alice   # show files

Consult info find for more information.

To accelerate file search, you can generate a database of all filenames on you filesystem:

updatedb

And then use the command

locate PATTERN

Note that the locate will return all files where PATTERN matches any substring in the full pathname (including directories).

Search files by content

grep PATTERN file

where PATTERN is a regular expression (See man grep).

To search files recursively in subdirectories, you can combine find and grep:

find -type f -name "*.tex" -print0 | xargs -0 grep -n PATTERN

But this is complex! An interesting alternative is to use ack (https://beyondgrep.com/). By default, it does a recursive search and it can focus on certain file types.

ack --python -w TOKEN  # search only python file matching on word 'TOKEN'

To install ack under ubundu:

sudo apt install ack-grep

Another search tool, which I have not used but is said to be faster than ack is ag http://conqueringthecommandline.com/book/ack_ag:

sudo apt install silversearcher-ag

Tools like grep and ack are useful to search within text files but pretty useless for binary files. If you want to search within .pdf or .doc files, you first need to extract the textual content and then index it. Then, you will be able to search files by their content. To this end, you can install and use a tool like recoll (see http://www.lesbonscomptes.com/recoll/). One issue though it that the index can quickly grow very large.

Display subdirectories as a tree

tree -d
tree -d -L 2   # limit depth to 2

Comparing two files or two directories

To compare two directories:

diff -r --brief dir1 dir2

To list all the lines that differ between file1 and file2:

diff file1 file2

For text files where the wrapping of paragraph may have changed, use wdiff.

meld provides a nicer, graphical way to show the differences between two files or two directories.

meld file1 file2

To create a patch listing the changes from version1 to version2:

diff -aur version1 version2 >dir2.diff

To apply the patch to version1 and generate version2:

  patch -p1 <dir2.diff

Synchronize two directories

To copy the content of dir1 into dir2 without the copying the files that already exist and are the same, use rsync:

rsync -a dir1/ dir2

If you want to copy the newest files and delete the ones (make dir2 a mirror copy of dir1:)

rsync -a --delete dir1/ dir2

rsync compares the files' contents which can be quite slow. You can considerably speed up the transfer if you accept that files with the same file sizes are considered unchanged:

rsync -r --size-only dir1/ dir2

To synchronize two directories (in both directions), I use the program unison, which keeps two directories synchronized, transfering only new or modified files, in both directions:

unison localdir ssh://remotehost/remotedir

Use git to keep an history of your projects and collaborate

Another approach to synchronise dirs is to use git repositories.

Learn about git by reading https://git-scm.com/book/en/v2

See also git-annex

Create a copy of a local git repository on github.com

git push --mirror git@github.com:username/project.git

Add a directory to the PATH

Most commands that you can execute from the command line are compiled programs or scripts. The shell (the program with which you are interacting most of the time with when typing commands in the terminal) searches for these programs in a list of directories. This list is stored in an environment variable called PATH. You can display its content:

echo $PATH

Note that when several directories contain a program with the same name, the first directory listed in the PATH variable has priority.

It is possible to find out which directory contains a given command by typing:

which command

Beware that an alias may shadow the command. It is therefore more informative to type

type -all command

To add a new directory newdir to the list in PATH, type:

export PATH="newdir":"$PATH"

Add this line to the file $HOME/.profile (on a Debian-based linux like Ubuntu) and source it:

. .profile

The following three functions, to be added to your ~/.profile or ~/.bashrc, allow you to edit the PATH on the command line by removing, adding or substituting strings within the PATH variable.

path_unset(){  # remove a directory from PATH
   pattern=$1
   PATH=$(echo $PATH | sed -e "s/[^:]*${pattern}[^:]*//")
}

path_sub(){  # substitute a substring in PATH
    from=$1
    to=$2
    PATH=$(echo $PATH | sed -e "s/${from}/${to}/")
}

pathmunge () {  # add a directory to PATH if it not already there
    if ! echo $PATH | /bin/egrep -q "(^|:)$1($|:)" ; then
       if [ "$2" = "after" ] ; then
          PATH=$PATH:$1
       else
          PATH=$1:$PATH
       fi
    fi
}

Finally, there is remarkable set of functions that allow you to bookmark and jump directly to subfolders: see dirb at https://github.com/icyfork/dirb.

In case your SHELL is tsch or csh instead of bash, type:

set path = (newdir $path)
rehash

Place these lines in the file ~/.cshrc , to have the correct PATH the next time you open a shell.

Startup files

Anything that should be available to graphical applications OR to sh (or bash invoked as sh) MUST be in ~/.profile

  • ~/.bash_profileshould just load .profile and .bashrc (in that order)
  • ~/.profile has the stuff NOT specifically related to bash, such as environment variables (PATH and friends)
  • ~/.bashrc has anything you'd want at an interactive command line. Command prompt, EDITOR variable, bash aliases
  • Ensure that ~/.bash_login does not exist.

(from https://superuser.com/questions/789448/choosing-between-bashrc-pandrofile-bash-profile-etc)

Disable the Touchpad while typing

killall syndaemon
syndaemon -i 1 -KRd

Unfreeze the mouse

sudo rmmod psmouse
sudo modprobe promise

The system is not responding

Try Ctrl-Alt-F1 to open a terminal. From there, you might be able to do:

sudo shutdown now

Alternatively, press Alt+PrintScr, and, keeping this key pressed, type, slowly, reisub. This mysterious sequence is explained at https://linuxconfig.org/how-to-enable-all-sysrq-functions-on-linux#h6-the-sysrq-magic-key

change the brightness of the display

xbacklight -set 50

or

xrandr --output eDP1 --brightness 0.5

Lock the screen under X11

Assuming that xscreensaver is running in the background.

xscreensaver-command -lock

or:

i3lock -d 30 # if you use i3wm

Suspend to RAM

sudo pm-suspend

Manipulating Images

Make sure to have ImageMagick installed (e.g. sudo apt install imagemagick on a Debian-based system)

To display an image (gif, .jpg, .png, .tiff, eps, ...)use:

display file.gif
eog image.png

To convert from one format to another:

convert file.jpg file.png

To resize an image:

convert img.png -resize 66%  img_small.png

To juxtapose several images:

montage -tile 4x4  *.png -geometry 1024x768 output.png

To superimpose images:

composite img1.png img2.png result.png

For more complex manipulations of bitmap image, I use The Gimp:

gimp file.jpg

To manipulate photographs, I like (Lightzone)[http://lightzoneproject.org/]

Diaporama:

feh

Creating graphics

l To edit vector graphics files, e.g. .svg:

inkscape

To draw graphs:

dot

To plot data, I use R or IPython:

import matplotlib.pyplot as plt
import numpy as np

Take a screenshot

To take a snapshot, that is, copy a portion of the screen into an image file, you can use ImageMagick's command import:

import file.png

You will then be able to select a rectangle on the screen with the mouse, which will be copied in file.png.

Other screenshot programs include gnome-screenshot, ksnapshot, scrot, maim... See https://wiki.archlinux.org/index.php/Screen_capture for a list.

Make a screencast

Voir http://www.linuxlinks.com/article/20090720142023520/Screencasting.html

Under i3, see https://github.com/synaptiko/.files/blob/4a6a549dfe0c22d19f38e32129b5c05de2bb6d34/i3/record-screen.sh

To create a symbolic link (somewhat similar to a 'shortcut' in Windows):

ln -s filename newname

If you delete or move the file, the symbolic links will be 'dangling'.

To find and remove dangling links in a directory:

symlinks -rd directory

Convert a directory into a single file

Say you want to all the files in a directory in an email attachment. You can put a whole directory into a file ``file.tar'' with the command:

tar cf file.tar directory

Before sending it, it a good idea to compress ``file.tar'', as described in the next section.

Compress / uncompress files

To compressing a single file:

gzip file

To decompress it:

gunzip file.gz

Better compression can be achieved with xz, which has the same syntax as gz:

xz file  # compress
unxz file.xz  # uncompress

To compress a full directory:

tar czf aga.tar.gz directory # compressing
tar tzf aga.tar.gz # listing
tar xf aga.tar directory # uncompressing

Other popular formats are .zip and rar:

zip -r archivename directory
unzip -l archivename.zip
unzip archivename.zip

rar file
unrar file.rar

Convert text files from DOS, Windows, Mac...

Texts files under unix, mac, dos and windows use differents codes for end-of-lines and accentuated characters.

To detect the character encoding, one can use uchardet

uchardet file.txt

Once you have determined the character encoding, you can use iconv or recodeto convert the file. `iconv`` is often installed by default.

iconv -f ISO-8859-1 -t UTF-8 file.txt > file.utf-8.txt
iconv -f WINDOWS-1252 -t UTF-8 file.txt > file.utf-8.txt

The recode program has a nice info documentation. By default, it does the transformation in place:

To convert file.txt coming from a Macintosh:

recode mac..latin1 file.txt

To convert from DOS codepage 850 to unix latin1:

recode 850..latin1 file.txt

To just remove \^ M:

recode l1/crlf..l1 file.txt

To convert from Windows codepage 1250 to unix latin 1 (iso-8859-1):

recode ms-ee..l1 file.txt

Substitute strings in many files

perl -pi.bak -e 's/OLDSTING/NEWSTRING/g' FILELIST
# attention: to match words only, use s/\bOLDSTRING\b/NEWSTRING/g

Compute word frequencies in a text file

To compute the number of occurences of words in a file, say alice.txt:

tr -cs A-Za-z\' '\n' alice.txt | tr A-Z a-z | sort | uniq -c | sort -k1,1nr -k2 | head -10

    1637 the
    1083 '
    872 and
    730 to
    631 a
    540 she
    528 it
    513 of
    460 said
    410 i

Run a command on multiple files

It is sometime useful to run a command on many files. The shell bash provides 'for' loops:

for f in *.eps; do convert $f ${f%.eps}.jpg; done  # convert .eps files in the current directory into .jpg

Note that this is only valid if you are interacting with the shell 'Bash'. If you use another shell then you must type 'bash' first.

Count the number of files in a directory

To know how many files with extension .img are in the current directory:

ls *.img | wc -l

If you want to include all subdirectories:

find -type f -name '*.img' | wc -l

List files and subdirectories

ls
ls -1 # in one column
ls -l # with detailed format
ls -d # only directories
ls -l --sort=time | head  # most recent files only

Create subdirectories

mkdir -p subdirname

Copy, rename, move or delete files

To copy a file in the same directory, giving it name2:

cp file1 file2

To copy a file from the current directory to the existing directory dir:

cp file1 dir

To rename a file:

mv file1 file2

To move a file to the existing directory dir:

mv file1 dir

To delete a file:

rm file

To avoid being asked for confirmation:

 rm -f file

Copy, move or delete directories

To create a new directory:

mkdir newdir

To copy the directory 'dir' in the destination directory 'destdir':

cp -a dir destdir

(Note: the '-a' option does a recursive copy - that is includes the subdirectories - and preserves the attributes of files)

To move the whole directory 'dir' inside the existing 'destdir':

mv dir1 destdir

To rename directory 'dir' as 'dir2':

mv dir dir2

To delete the directory 'dir' and all its content:

rm -rf dir

Renaming files, replacing their name by their creation date

#! /bin/bash

for fullfile in "$@";
do
    filename=$(basename "$fullfile")
    extension="${filename##*.}"
    filename="${filename%.*}"
mv -n "$fullfile" "$(date -r "$fullfile" +"%Y%m%d_%H%M%S").${extension}";
done

Check or modify the rights of access to a file or a directory

When you use ls -l to list the files in a directory, the first string of characters, made of 'x', 'r' 'w', '-'... specifies the access rights (Consult Understanding file permissions on Unix: a brief tutorial)

To allow everybody to read all the files in the current directory:

chmod a+r *

If, when using ls -l, there is a + sign is trailing the rights, it means that ACL (Access Control List), is set on the files or directories. The chmod command will not work: you must then use the getfacl and setfacl commands to list or modify the access/write rigths

To avoid copying a file in several places on the same disk, it is a better idea to use a link:

ln existingname newname

Thus the same file can have several names (and be in several directories at the same time).

Who am I?

As far a the computer is concerned, the identity of the current user (that is its login), can be printed with:

whoami

Note that your login name, home directory, and shell are saved in the environment variables LOGNAME, HOME and shell:

echo $LOGNAME $HOME $SHELL

Change your identity

To temporally become newuser:

su - newuser

Of course, you will be prompted for newuser's password.

If you want to become root:

sudo -i

When you are done, type:

exit

Each login is associated to a UserID (UID), an integer, an to list of GroupIDs (GUID). You can list the information linked to the current login:

id

It is sometimes necessary to change your UID number, for example when you swap an external hardrive with a unix filesystem. Here is how to do it:

usermod -u <NEWUID> <LOGIN>
groupmod -g <NEWGID> <GROUP>
find / -user <OLDUID> -exec chown -h <NEWUID> {} \;
find / -group <OLDGID> -exec chgrp -h <NEWGID> {} \;
usermod -g <NEWGID> <LOGIN>

Change group

Check which groups you belong to using id, then use

newgrp  group

From now, the files and directories you create will belong to group group

To modify the group of already existing files in directory dir:

chgrp -R group dir

Which computer/system am I currently working on?

To display the network node name (also called the ``hostname''):

uname -a

The following also works:

hostname

Check who is logged on the computer

To see who is currently logged on the system, use

who

or

w

If you are superuser, you can see a journal of the logins with the command:

last

Connect to a remote computer

A secure method to connect to a remote computer:

ssh computername

or

ssh login@computer

Note that the remote computer must be running a 'sshd' server.

In the good old days, it was possible to connect with the commands:

rlogin computername
telnet computername

Note that the login and password were sent in clear over the network, and that is why ssh is prefered nowadays.

Execute commands on a remote computer, without login

ssh login@computername command

Keeping a remote session alive

Once connected on the remote computer, execute:

tmux

When you want to leave, press Ctrl-b d. The terminal is detached but not closed.

Next time you connect to this remote computer, to continue your work, you can access the session:

tmux a

See https://danielmiessler.com/study/tmux/ for a primer on tmux.

Copy files to or from a remote computer

scp -r localdir remotelogin@remotecomputer:remotedir

rsync -avh localdir/ remotelogin@remotecomputer:remotedir

tar  -cf - dir | ssh login@remotehost tar -xvf -

To synchronize bidirectionnaly:

unison

To 'aspire' web pages:

wget  address
curl  address

If you need to use ftp, you can use the following clients

ncftp
lftp

Setting up SSH

To avoid having to type your login password each time you use ssh or scp, you can setup SSH to use public and private keys to perform the authentification automagically.

First, you must generate keyfiles, once, on your local computer. To do so:

ssh-keygen

This generates, among other files, a public key stored in a file ~/.ssh/identity.pub). You now need to copy this key in the authorized_keys file inside the ~/.ssh directory of the remote computer you want to connect to.

ssh-copy-id  remotecomputer

If you have let an empty passphrase, you can know use ssh or scp without entering your password. But so can do anyone who access your account on your local computer.

So you may prefer to use a passphrase. To avoid having to type it each time you log to the remote computer, copy the following lines in your ~/.bash_profile:

eval `ssh-agent`
ssh-add < /dev/null

You will be prompted for the passphrase only once: when you login on the local computer (See the explanations about ssh-agent at http://mah.everybody.org/docs/ssh).

Display locally the interface of an XWindow program running on a remote computer

The X Window graphic system used by Linux allows to see on the local computer graphic windows generated by a program running on a remote computer.

On the local computer, type:

xhost +

On the remote computer, type:

export DISPLAY=localname:0   # if the shell is bash

or

setenv DISPLAY localname:0  # if the shell is a csh derivative

Replace localname by the name of local computer. If you do not know it, type the following on the local computer:

uname -n

Setting up X11 forwarding with ssh

To allow graphical applications ran on the server to display their windows on the local computer, when using ssh:

From https://unix.stackexchange.com/questions/12755/how-to-forward-x-over-ssh-to-run-graphics-applications-remotely

X11 forwarding needs to be enabled on both the client side and the server side.

On the client side, the -X (capital X) option to ssh enables X11 forwarding, and you can make this the default (for all connections or for a specific conection) with ForwardX11 yes in ~/.ssh/config.

On the server side, X11Forwarding yes must specified in /etc/ssh/sshd_config. Note that the default is no forwarding (some distributions turn it on in their default /etc/ssh/sshd_config), and that the user cannot override this setting.

The xauth program must be installed on the server side. If there are any X11 programs there, it's very likely that xauth will be there. In the unlikely case xauth was installed in a nonstandard location, it can be called through ~/.ssh/rc (on the server!).

Note that you do not need to set any environment variables on the server. DISPLAY and XAUTHORITY will automatically be set to their proper values. If you run ssh and DISPLAY is not set, it means ssh is not forwarding the X11 connection.

To confirm that ssh is forwarding X11, check for a line containing Requesting X11 forwarding in the ssh -v -X output. Note that the server won't reply either way, a security precaution of hiding details from potential attackers.

Modify the password

To change your password a local system:

passwd

To change your password on a network administrated with NIS (``yellowpages''):

yppasswd

Change the login shell

To change your password on the local system:

passwd

To change your login shell, e.g. from /bin/csh to /bin/bash:

ypchsh

or

chsh -s /bin/bash

Access files on a data CD or on a floppy

With some linux systems, you just insert the CD or the floppy and the content become available in the directory /mnt/cdrom or /mnt/floppy:

ls /mnt/cdrom
ls /mnt/floppy

If the floppy is not write-protected, you can create or copy files in /mnt/floppy just like in any ordinary folder.

Note that if you have several cdrom or floppy drives, they may have names cdrom1, cdrom2, floppy1,...

In some Linux systems, it is necessary to manually mount the cdrom or the floppy before accessing the files, and umount it before ejecting it. For the cdrom:

mount /mnt/cdrom
ls /mnt/cdrom
...
umount /mnt/cdrom
eject

For the floppy:

mount /mnt/floppy
ls /mnt/floppy
umount /mnt/floppy

If you get an error message like mount: only root can do that, ask the system administrator to grant you right to mount floppies by adding the user option the configuration file /etc/fstab. More information in the manual pages of mount and fstab:

man mount
man fstab

Concerning floppies, some systems have mtools installed (see man mtools') which provide themdirandmcopycommands that emulate the old DOS commandsdirandcopy`. It is not necessary to mount the floppy to use them.

Format a floppy

To format the floppy with an ext2 filesystem, and mount it:

fdformat /dev/fd0
mkfs -t ext2 /dev/fd0
mount -t ext2 /dev/fd0 /mnt/floppy

This floppy can be read only on other linux systems. To be able to read it under Windows/DOS, you should use a DOS filesystem with mkdosfs in place of mkfs -t ext2:

mkdosfs /dev/fd0

Split a large file on several floppies

First compress the file, with gzip or bzip2 (see section41). If it still does not fit on a single floppy (1.4Mb), you can use the command split:

split -b1m file

This create a series of x?? files which you can copy on separate floppies.

To reassemble the files:

cat x* >file

Rip sound files from an audio CD

On, the command line, you can use cdparanoia. For example, to rip an entire audio CD:

cdparanoia -B

To rip just one track:

cdparanoia -w track_number file.wav

Maybe an easier way to copy tracks from an audio cd it to open konqueror, and type 'audiocd:/' in the address bar. This will show you the content of the CD, which you can copy somewhere else. Copying from the mp3 or ogg folders will do the automatic translations for you.

Else, there are various programs with graphical interface which allow you to rip audio CD: grip and kaudiocreator, rhythmbox.

Convert from wav to mp3

I use lame:

lame file.wav file.mp3

Convert from wav to ogg vorbis

I use oggenc:

oggenc file.wav -o file.ogg

Create a data CD

  1. Put all the files you want to save in a given directory, e.g. /tmp/mycd.
  2. Create an iso image:

    mkisofs -o cd.iso -J -R /tmp/mycd
    ls -l cd.iso
    

    Check that the resulting file cd.iso file is not too large to fit on the CD; if it less than 650Mb, this should be ok.

  3. Record on the cd (you must be root).

    You must know which is the device is associated to the CD writer drive.

    cdrecord -scanbus
    

    To determine the x,y,z scsi coordinates of your cd writer. If it does not appear listed, it may be because the ide-scsi parameter was no passed to the Linux kernel (See the HOWTO about CD Writing).

    To record, do:

    cdrecord dev=x,y,z -multi speed=0 -data cd.iso
    

Create an audio CD

To put on an audio CD all the *.wav files which are in the current directory:

cdrecord dev=x,y,z -pad speed=0 -audio *.wav

(x,y,z must be replaced by the numbers returned by cdrecord -scanbus)

Make backups

You can write backup scripts rsync but it has already been done many time. I recommend backintime

Connect to a bluetooth device

sudo service bluetooth start
sudo service bluetooth status

rfkill list
rfkill unlock 0:


bluetoothctl
 power on
 devices
 scan on
 pair XXXXXXX
 connect XXXXXX

List the hosts in a NIS domain

If you are connected on a local network administrated by NIS (``yellow pages''), you can display the list of other computers on the network:

ypcat hosts

Mounting a Samba Share

Assuming you have a SAMBA server with IP 192.168.0.50

smbclient -L 192.168.0.50
sudo mount -t cifs //192.168.0.50/BACKUPS /mnt -o username=chrplr,file_mode=0777,dir_mode=0777

Which shell is running?

When you enter commands on the command line in a terminal, the text you type is interpreted by a program called the 'shell'. There are different shells that speak different dialects. To determine the shell you are communicating with, type:

echo $SHELL

Note: this does not work well for subshells:

bash
echo $SHELL
csh
echo $SHELL
exit
exit

Create a script to execute a series of commands

If you happen to often type the same series of commands, it is a good idea to create a script.

If it does not exist yet, create the directory \$HOME/bin.

Use a text editor to create a file 'myscript' in this directory, and type the series of commands.

The first line of the file should be:

#! /bin/bash

Save the file, then enter the command:

chmod +x ~/bin/myscript

You can now type ``myscript'' on the command line to execture the series of commands.

To go further, you should learn how to use arguments to scripts. There are tutorials on shell script programming on the web.

Get help. Find manuals

Many commands have associated ``man pages''. To read the man page associated, for example, to the command 'cp':

man cp

Some commands also have manuals in the form of 'info files':

info gawk

On many linux systems, there is additional documentation in the /usr/share/doc folder. The HOWTOs can be especially helpful.

Cut'n paste

Cutting & pasting under linux is not always straigtfoward. This is due to the fact that there are various systems of cut'n paste cohabitating.

To copy text, the following works with most applications:

  • Click the left button and drag the cursor over the text to be copied.
  • Click on the middle button to paste.

Note that this is very convenient: there no need to explicitly 'copy' the text.

If you use the window manager 'kde', there is a useful applet called 'klipper' located on the panel. Klipper keeps copies of the most recent clipboard contents. If a cut'n paste operation does not work, you may open klipper, select the relevant line, and retry to paste. It usually works.

If it does not work, then you can try the Cut/Copy/Paste functions from the applications' menus. Sometimes, it is necessary to save the region as a file in the first application, and insert this file in the second application.

Mount a partition of a usb drive

Insert the USB drive, use dmesg to see the partitions, then use pmount or udisk ctl

dmesg

pmount /dev/sdb1
udisksctl mount -b /dev/sdb1

Setup an ethernet card to access the internet

You need to know IP, MASK, GATEWAY, DNS, HOSTNAME and DOMAIN:

ifconfig eth0 IP netmask MASK up
route add -net default gw GATEWAY netmask 0.0.0.0 eth0
hostname HOSTNAME
echo ``domain DOMAIN'' >/etc/resolv.conf
echo "nameserver DNS" >>/etc/resolv.conf

Changing/Editing network connection

nmtui  # text mode
nmcli  # text mode
unity-control-center

Dynamic libraries

To run, some programs need to access functions in dynamic libraries. Dynamic libraries have the extension .so. They are located in /lib, /usr/lib, /usr/local/lib...

To list the libraries needed by a program:

ldd program

After adding new a new dynamic library, e.g. in /usr/local/lib, you must run, as superuser:

ldconfig -n /usr/local/lib

It is possible, as a user, to tell linux to search libraries in a particular place, using the LD_LIBRARY_PATH variable. For more information about how dynamic libraries are accessed, consult the manual of ld.so:

man ld.so

Install new software

If it come as a .tar.gz and contain a configure script

tar xzf package.tar.gz
cd package
./configure --prefix=$HOME & make & make install

This install the software in your home directory. To install it for every user, you need to omit the prefix option and be root when calling ``make install''.

If you are on a apt-based system (Debian, Ubuntu):

sudo apt install packagename

If you have the .deb file:

sudo dpkg -i file.deb

If you are on a rpm-based linux system, to install an rpm file:

rpm -i package.rpm

To check if the package is correctly installed:

rpm -V package

To remove it:

rpm -e package

Check if a software package is installed

To check if, say, ghostscript is installed:

rpm -q ghostscript

You can get the list of all installed packages:

rpm -qa

Configure Multiple Displays

Use the programs xranrd and arandr

xrandr --output eDP1 --rotate left

Get back your sanity with a productive environment

The following works for me.

  • Use a window manager that allows you that launch applications pinned on some workspace and to have the workspaces accessible by a fixed keystroke. The tiling window manager i3wm fits the bill.
  • use Emacs/Spacemacs as an editor
  • Use Linux rather than Windows
  • use anaconda3 for Python
  • use git for projects

Common file types


typical extension file type application(s)

txt text or ascii file cat, less (view) vim, emacs (edit)

pdf Adobe PDF acroread, xpdf, evince, okular (view)

ps, eps postscript gv (view) pstops (rearrange) ps2pdf (convert)

html, htm web page links, konqueror, mozilla (view) soffice (create)

png, jpg, gif... graphic files display (view) import (snapshot) convert (convert) gimp (manipulate)

doc, xls, ppt Office document soffice

sxc, sxi, sxw OpenOffice document soffice

tex TeX and LaTeX documentz tex, latex, pdflatex (process)

dvi Dvi documents xdvi (view) dvips, dvipdf (convert to ps or pdf)

gz, Z, xz, bzip Compressed file gunzip, xz, unxz, zip, bunzip2, bzip2

tar tar archive tar tf (view) tar xf (extract) tar cf (create)

tar.gz compressed archive tar xzf (extract)

tar.bz2 Compressed tar archive tar xjf

zip zip archive unzip -l (view) unzip (extract) zip (create)


[^1]: Links to learn to use the command line: