Linux tidbits

Regular commands I use every day in Linux plus a few eclectic ones. Basically geared to the new user. Tips or thoughts, please let me know.

Man pages

In Linux there is a manual for just about anything. Learn about almost everything by “man command” in the terminal. (e.g. man ls). Or type “command –help” for a basic description. Also, many man pages also cover configuration files (man resolv.conf).

Basic Commands

Navigating:

• Up key– Command History
• Tab – Auto-completion, nice and handy for completing file-names, directory names, and commands.
• Commands are in this form: command -arguments

Files ( + directories )

• ls ( list ), -l ( long ), -a ( shows hidden )
• cp ( copy )
• mv ( move or rename ), mv filename1 filename2
• rm ( remove ) Very dangerous to use as root. Use with caution. -r ( recursive ) -f ( force – needed to remove a link)

Wildcards to expand definitions:

• * (matches any character), cp *.txt ~/Desktop
• ? (matches any single character), cp file?.txt ~/Desktop
• [characters] (Matches a range/set of characters), cp [a-n]*.txt ~/Desktop</li>
• [!characters] (Matches any character that is not a member of the set characters)

Directories

cd    #( change directory )
pwd   #( print working directory )
mkdir #( make directory )

A name followed by a / means it’s a directory, bash will figure it out if you don’t use it but some apps don’t. A safe syntax would be cd myfiles/

Command Output to Text (Standard Output)

ls /usr/bin > /home/user/Desktop/programs.txt

Add to an existing text file (append):

ls /sbin >> /home/user/Desktop/programs.txt

Pipes ( | )

Useful for using programs in conjunction with others:

ls -l | less

Filters

Popular filters used after piping:

• sort – alpha-numeric ordering
• uniq – removes duplicate lines of data
• grep – returns the output of a specified pattern of characters
• head, tail – outputs the first of last lines of output
• tr – translates characters – can be used for upper/lower case conversion

Use grep to extract patterns from files

grep EE /var/log/Xorg.0.log
ls ~/Documents | grep recipe
glxinfo | grep -i direct

Files and File Permissions

View file permissions

List the files in “long” view:

ls -l

-rwxr--r-- 1 user user 225444 2007-05-01 21:58 abc.pdf
||  |  |     |    |
||  |  world |    group name
||  group    owner name
|owner/user
directory

r = read = 4
w = write = 2
x = executable = 1

Change File Permissions

owner = rwx = 4+2+1 = 7; group = r = 4 ...

The above file’s permissions numerically is 744. To change permissions of the above file:

chmod 750 abc.pdf

Change Ownership

chown user:group /home/user/document.txt

Lazy way of make a file executable ;)

chmod +x ~/.scripts/example

File Systems

Show all partitions and their types:

sudo fdisk -l

Show mounted partitions used/available space:

df -h | grep ^/dev

See all file systems mounted::

cat /proc/mounts

Sort Directories by How much space they consume:

du | sort -nr

Define Disks and Partitions and how they mount

sudo mkdir /mnt/USB-Drive

sudo mount -t vfat -o rw /mnt/USB-Drive

types include hfsplus, vfat…

The fstab file defines how to mount available disks/partitions that can automatically be mounted it at boot: Enter in /etc/fstab:

/dev/sda2    /mnt/OSX          hfsplus ro,exec,auto,users    0      0
/dev/sda4    /mnt/Shared_Disk  vfat users,auto,uid=1000,gid=100,umask=007  0 0

ro – read-only, rw – read-write, auto mounts filesystem on boot

If the disk will resemble another disk it is better to use a unique device ID (UUID) rather than /dev/disk:

sudo blkid /dev/disk

Unmount all possible file systems:

umount -a

File System Check

Only filesystems that are able to be unmounted can have the filesystem checked.

Reboot immediately and check for errors:

sudo shutdown -Fr now

For specific mounted filesystems they can be check on next boot by placing a forcefsck file at the root of the disk/partition:

sudo touch /forcefsck
sudo touch /home/forcefsck

This will not run a file system check though if the file system is marked clean. For this boot a rescue disk and run fsck -f to do this.

Change how often fsck runs at boot (-c = count boots, -i = time interval):

sudo tune2fs -c 30 -i 6m /dev/disk

Check and mark bad blocks on damaged drives:

fsck -vcck /dev/disk

Mounted file systems should be checked from the Installer CD/DVD or on boot.

Swap

Create swapfile

dd if=/dev/zero of=/swapfile bs=1024 count=2097152

Swap is recommended to be 1-1/2 to 2x the value of the RAM to use for hibernation.

1 GB = 1024 MB = 1024 x 1024 kB = 1048576 kB = 1048576 kB x 1024 bytes/kB = 1,073,741,800 bytes10

mkswap /swapfile
swapon /swapfile

Add to /etc/fstab:

/swapfile              swap             none     defaults

Controlling Swap

Turn off swap:

swapoff -a /swapfile

Swapiness is the input/output priority of swap. To measure the current value:

cat /proc/sys/vm/swappiness

To change the swap priority (higher value means more swapping):

sudo sysctl vm.swappiness=10

to use this value permanently add it to /etc/sysctl.conf (vm.swappiness=0). Values of 20 or lower are better for laptops.

File Compression

Pack:

tar gunzip:
tar cvpzf /AreaToSaveTo/yourcompressedfile.tgz --exclude=/this/folderorfile /CompressionStarts/Here

tar.bz2(tbz2) (block sorted, better compression):
tar -cvjf files.tar.bz2 fileorfolder
bzcat linux-2.6.XX.tar.bz2 | tar x

Unpack:

tar xvf file.tgz

unrar e file.part01.rar

Span Multiple Volumes

Create:

tar -c -M --tape-length=2294900 --file=part1.tar too-large-archive.tgz

Extract:

tar -x -M --file=part1.tar too-large-archive.tgz

At prompt specify new (n),
then specify volume name (e.g. n part2.tar)
tape-length is 1024 bytes measurement or (1 computer kilo)

Or use “split” to break a large volume (2m = 2 megabytes, LF is the prefix for new name):

split -b 2m largefile LF_

tar -cvj /full/path/to/mybigfile | split -b 650m

Put back together:

cat file* > newfile

Backup and Restore

Tar – From Install CD

cd /mnt/distro
tar -czpvf /mnt/distro/macbook_distro_date.tgz *

Rsync – Full Backup

rsync -avtp --delete --exclude=/home/user/somedir /source/dir /destination/dir

• -a archive, -v verbose
• -t preserve modification times, -p permissions
• --delete removes destination file if has been removed from source
• --links recreate symlinks
• -z compress from source to destination – good for slow connections.
• use “-a e ssh source name@hostname:dest” for ssh

Users

Add user

useradd -m -G adm,audio,cdrom,cdrw,cron,games,plugdev,portage,shutdown,usb,users,video,wheel -s /bin/bash user

Groups may vary some per distribution. Some groups will not be available until a certain program is installed.

Add/delete user to group:

gpasswd -a user plugdev
gpasswd -d user plugdev

See what groups user belongs to:

id

Remove user:

userdel username

CD/DVD

Writing to CD/DVD with Rock-Ridge support

Rock-ridge support add Unix file extensions and attributes for iso9660 standard disks.
DVD are marked as 4.7GB capacity but thats just the marketing measure. In terms the computer understand the space on a DVD is 4.368 GB’s (1 GB = 1048576 kB x 1024 bytes/kB). DVD +R at 4x or 8x for best performance

DVD

growisofs -Z -lrJ -joliet-long /path/to/files

• -Z means to start at the beginning of the dvd
• –l allows long filenames (breaks DOS compatability)
• –r Rock-ridge support
• -J Add Joiliet support
• -joliet-long – allows Joliet filenames to be 103 characters long instead of 64 – breaks joliet compatibility but works in most cases.

CD

mkisofs -o my.iso -lrJ /path/to/files

Then burn iso to CD (not sure if I can write directly to CD, from what I’ve seen it would seem that I can’t).

Blanking a Disk
If you want to blank a disk or it already has a file-system on it you’ll see an error like “WARNING /dev/hda already carries isofs!” then reinitialize the filesystem:

DVD

dvd+rw-format -f /dev/sr0
growisofs -Z /dev/hda=/dev/zero

CD

cdrecord -v dev=/dev/hda blank=fast
cdrecord -v dev=/dev/hda speed=2 blank=fast
cdrecord -vv dev=1,0 blank=all

ISO

Write ISO to CD/Drive:

dd if=name.iso of=/dev/sdb1

Mount ISO:

mount -t iso9660 -o loop,ro name.iso

Create an ISO from a DVD or CD:

dd if=/dev/sr0 of=name.iso

Create and ISO from a file/directory:

mkisofs -o name.iso /path/to/file_or_directory

CDRWin (.bin/.cue) images to ISO:

bchunk name.bin name.cue name.iso
bin2iso name.cue

Converting CloneCD images to ISO:

ccd2iso name.img name.iso

Converting nrg (Nero) images to ISO:

nrg2iso name.nrg name.iso

Support for writting large file sizes

ISO has file size limit of 4GB (untested -udf support is still in alpha):

mkisofs -o my.iso -lrJ -allow-limited-size -udf file-or-pathtofiles
growisofo -Z /dev/sr0 -lrJ -allow-limited-size -udf file-or-pathtofiles

Mouse/Keyboard

Change keymaps:

setxkbmap dvorak

Map pointer buttons to keyboard:

xmodmap -e 'keycode 116 = Pointer_Button2'
xmodmap -e 'keycode 108 = Pointer_Button3' 
xkbset exp m

Hardware Info

Kernel messages about hardware

dmesg | less

Cpu info:

cat /proc/cpuinfo

List all PCI/USB devices

lspci
lsusb

Detect hardware as it’s plugged in

sudo tail -f /var/log/messages

lshal –monitor # more detail

Icons / Cursors / Fonts …

Reset Icon Cache

gtk-update-icon-cache -f /usr/share/icons/hicolor/

Convert Windows Icons to Linux

broken ink

Reset cache for fonts:

fc-cache -vf

Build font info per directory:

mkfontscale
mkfontdir

Take screenshot of selected area

import filename.png

Set gamma

If you have ability to calibrate your own icc profile (Macintosh’s do) copy the icc profile to Linux and use “xcalib icc.profile“, otherwise a basic gamma can be set:

xgamma -bgamma 0.925 -ggamma 0.925 -rgamma 0.925

System

Shutdown at a specific time

shutdown -h 22:33
shutdown -P now

date

Use “date” to check date and to set system clock:

date MonthDayHourMinuteYear

Find out kernel version:

uname -r

Start Program that isn’t in the Systems Path

Only programs that are in a system’s $PATH setting can be started by typing the command, otherwise:

./program

Disable Touchpad whilest Typing

syndaemon -d -t -i 2

Networking

Samba

Change or add password to smbconf:

sudo smbpasswd -L -a user

Mount SMB share to folder:

sudo smbmount //192.168.1.105/user/ mnt/directory -o username=username,password=pass,uid=1000,mask=000

Mount all Samba Shares in fstab:

mount -a -t smbfs

SSH/SCP

SSH Howto

Remote login with SSH with username (diferent than the one you’re using):

ssh -l username 192.168.1.101

Copy remote file to local file:

scp -p user@192.168.1.101:~/Desktop/file.name file.name

Download entire website:

wget -r http://www.example.com/

Advanced

Bash

The Bash configuration file (~/.bashrc) file:

Adding PATHs to the ~/.bashrc file will make the system aware of another folder that has executables and shortcuts can be created for common commands:

export PATH=$PATH:/home/user/.scripts:
alias capscreen="import ~/Desktop/screen.png"

To see the preset variables already defined for bash:

set

Search History

ctrl-r

Cron
Cron is the system program scheduler. It checks every minute for commands to run. To edit a crontab (cron jobs):

crontab -e

#   minute (0-59),
#   |   hour (0-23),
#   |   |   day of the month (1-31),
#   |   |   |   month of the year (1-12),
#   |   |   |   |   day of the week (0-6 with 0=Sunday).
#   |   |   |   |   |   user

43 08 * * * env DISPLAY=:0.0 audacious /home/user/My\ Music/Other/Alarms/301gq.mp3

chroot – (changing root)
Userful for logging into your current Linux from an installtion CD:

su
mkdir /mnt/osname
mount /dev/sda3 /mnt/osname
mount -t proc none /mnt/osname/proc
mount -o bind /dev /mnt/osname/dev
chroot /mnt/osname /bin/bash

Compile Kernel

make oldconfig
make menuconfig
make clean zImage modules modules_install install

For PPC “make pmac32_defconfig” will generate a basic config.

Find Kernel Modules:

find /lib/modules/*Kernel-Version* -type f -iname '*.o*' -or -iname '*.ko*'

Add the screen program to be able to background a terminal process
screen command (CTRL + A + D to background it, to return it: screen -r).

Use noup to continue a process even if you log out

noup command

Unsorted/Less Used

sudo echo >> no work

echo "my text" | sudo tee /etc/portage/package.use

See whats taking up ram:

ps auxf --sort size

Allow window executables to run directly (will need Wine and misc. binaries enabled in kernel)

In /etc/sysctl.conf add:

fs.binfmt_misc.register = :WINEXE:M::MZ::/usr/bin/wine:

and add to fstab:

none /proc/sys/fs/binfmt_misc  binfmt_misc  defaults 0 0

Re-size Images from the command line

Requires imagemagick to be installed (convert writes new image, mogrify overwrites):

convert image.jpg --resize 800x600 newresized.png
mogrify -geometry 1024x768 *.png

Copy ALL Files (+invisible, hard links, softlinks)

find . -depth -print0 | cpio -null -sparse -pvd /mnt/newhome/

Create random numbers, hex letters

dd if=/dev/random bs=1 count=5 2>/dev/null | xxd -ps

Run programs sequentially or concurrently

program1 && program2
program1 & program2

A simple web server

Share files in directory and all subfolders:

python -c "import SimpleHTTPServer;SimpleHTTPServer.test()"

View at http://localhost:8000 or http://your_ip:8000/.

Debian Specific:

drive space show taken by installed packages

dpkg-query -W --showformat='${Installed-Size;10}\t${Package}\n' | sort -k1,1n

Rebuild Font Directory

dpkg-reconfigure fontconfig