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Linux Tips

This page contains a selection of tips for Linux (and UNIX) that I have collected. It's more of a memo to myself and not intended as a guide or anything. So just see it as notes that I share with whoever is interested. Most of these tips are for the bash shell environment.

Manipulating command line instructions

replace "str1" by "str2" in previous command:

^str1^str2[^]

repeat event from 2 events ago:

!-2

repeat most recent event starting with "string":

!string

repeat most recent event containing "string":

!?string[?]

repeat the entire command line typed so far:

!#

Directory Contents

Directory listing including non-printable chars

ls -q *

list directory names not their contents

ls -d *

List all entries in current directory that are files (not directories), alternatively use find with the -depth option.

for i in *; do [ -f $i ] && echo $i; done

And inversely list only directories:

for i in *; do [ -d $i ] && echo $i; done

Directory Manipulation

Push current directory to directory stack:

pushd .

Pop directory from directory stack:

popd

System

Information about the system:

uname -a

How many cores does the system have:

grep "model name" /proc/cpuinfo | wc -l

Files

Viewing file with line numbers:

cat -n filename

"more" file starting at a certain linenumber:

more +linenumber filename

"more" file starting at a certain pattern:

more +/pattern filename

Rename all .htm files to .html in one go:

rename .htm .html *.htm

Destroy a file:

shred -uz filename

Mail

Mail a file as plain text:

mail -s "subject" e-mail_address < file

Mail an attachement (if uuencode present and in path):

uuencode attachment.txt | mail -s "subject" e-mail_address

Arithmetics

Do some quick maths (whole numbers only):

echo $((7*8+5))

Sorting

To sort based on a section of each line in a file use the --key argument. For instance to list countries in alphabetical order of name rather than their country code:

grep -v "^#" /usr/share/zoneinfo/iso3166.tab |sort --key=2.1

Processes

Display current processes

ps -ef|cut -c49-

Display the processes of user userid

ps -fu userid

Show the processes started on tty

ps -ft tty

Show the process with PID pid

ps -fp pid

Restarting a process with PID pid:

kill -HUP pid

Restarting sshd:

kill -s HUP $(cat /var/run/sshd.pid)

Editing ssh settings:

vi /etc/ssh/sshd_config

Changing (lowering) a running process' priority:

renice +10 -p pid

ftp

Commands you can use in an FTP session.

File permissions on target site:

site mask 133
site chmod 644 filename

Toggle interactive prompting of multiple arguments commands:

prompt

Status of current connection:

status

sftp and ssh

Setting up passwordless login for sftp and ssh:

ssh-keygen -t rsa
ssh-copy-id -i ~/.ssh/id_rsa.pub username@remote_host
sftp username@remote_host

Checking the last logins of the current user:

last -i | grep $USER

Last logins of all users on a machine:

last -i

misc

Run one instruction as user id:

su - id -c "instruction"

Display terminal settings:

stty -a

Display configuration of system variable:

getconf CHILD_MAX

Set tab-stop interval to 4 in the terminal:

tabs -4

tr

tr also works with these kind of constructions:

tr '[:lower:]' '[:upper:]'
Forgetting the 's (single quotes) will cause problems if there is a file in your current directory with the name: l, o, w, e, r, u, p or : Try touch u && echo tr [:lower:] [:upper:]

To remove CRs (^M) from ascii files ftp'd in binary mode from Windows to Linux. An EOF (^Z) remains at the end of the file.

tr -d '\r' < file_with_CR > file_without_CR

tar

Extract a single file from tar archive into the current directory, whitout needing to know the full path (obviously only works if the filename is unique):

tar -xf tarfile --transform='s,.*/,,' $(tar -tf tarfile | grep filename)

services / daemons

You need to be root to run these instructions:

Status of all services:

service --status-all

Restart a service (for example the network service) (similar with start or stop):

service network --full-restart

List all services settings for all runlevels:

chkconfig --list

Example: turn mysql deamon on for runlevels 2 to 5:

chkconfig mysqld on

With systemd

Status of all daemons:

systemctl

Restart the http daemon (stop and start also work):

systemctl restart httpd.service

Turn the http daemon on in default runlevel:

systemctl enable httpd.service

Stopping and starting gnome:

gdm-stop
gdm-start

yum

Run yum instructions as root:

Clean up packages downloaded by yum:

yum clean packages

Exclude a package from being updated, handy if a package is causing a missing dependency error:

yum update --exclude=package

Example to update everything except the kernel:

yum update --exclude=kernel*

Search for a package:

yum search word

Gnome Tricks

Make a screenshot of the window in focus in 5 seconds:

gnome-screenshot --window --delay=5

Flush the Gnome keyring passphrases from memory

gnome-keyring-daemon -r -d

Turn off screensaver and powersave mode (can also use dconf-editor):

gsettings set org.gnome.desktop.screensaver idle-activation-enabled false
gsettings set org.gnome.settings-daemon.plugins.power sleep-display-ac 0

DO NOT "set org.gnome.settings-daemon.plugins.power active false" this removes the battery icon.

FFmpeg and mencoder (Media Conversions)

ffmpeg can be used for all video and audio formats, these examples just use one as an example.

Convert a .mov file to a .flv file (-s optional resize):

ffmpeg -i input_filename.mov -s widthxheight output_filename.flv

Cut a section from an MP3 sound file (-t = total length of clip):

ffmpeg -i input_filename.mp3 -ss HH:MM:SS -t HH:MM:SS output_filename.mp3

Rotate a video clip:

mencoder -vf rotate=1 -ovc lavc -oac copy -o output.avi input.avi

Rotate right: rotate=1, rotate left: rotate=2

Extract sound from a .WebM video clip:

ffmpeg -i input_filename.webm -vn -acodec copy output_filename.ogg

Remove sound from a video file:

ffmpeg -i input_filename.webm -an output_filename.webm

Image to PDF conversion

Convert an image to a PDF document:

convert imagefile docname.pdf

You need to have imagemagick installed for the convert utility.

Creating a new user

To create a new user from the command line, log in as root

adduser username
passwd username

Internet based services

Look up the definition of a word (in English) from the command line:

curl dict://dict.org/d:word

 


Linux user 425492

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