====== Useful Linux Commands ======
The following is a list of useful commands that I've learned for Linux, but that I use so rarely, I tend to forget until I need them again.

===== CDROM / DVD commands =====

==== Mount an ISO to the filesystem ====

Execute the following command:
  mount file.iso /cdrom -t iso9660 -o loop

====Creating a CD ISO====

To rip an entire normal data-cd (ISO filesystem) from a CD-ROM:

  dd if=/dev/cdrom of=my_cd_image.iso

====Making an ISO from a file system====

To create an iso using files in Linux:

  mkisofs -o image.iso path/

====Burning a CDROM====

  wodim dev=/dev/cdrw -v -data cd_image.iso

  wodim dev=/dev/cdrw -v -audio [wav files...]

====Burning a DVD====

To burn a DVD from the filesystem:

  growisofs -dvd-compat -input-charset=ISO-8859-1 -Z /dev/cdrom -R -J -pad "/path/to/source/dir/structure"

=====Floppy Disk Commands =====

====Creating a floppy image====

To create a blank floppy disk image:

  mkfs.msdos -C image.flp 1440  

====Mount a floppy image to the filesystem====

To mount a floppy image:

  mount -o loop image.flp /media/floppy1/

=====Video codec commands=====

====Transcoding to iPod and iPhone format====

To take a video file to a format usable by an iPod or an iPhone:

   ffmpeg -vcodec xvid -b 300 -qmin 3 -qmax 5 -bufsize 4096 -g 300 -acodec aac -ab 96 \
      -i source_file.avi -s 320x240 -aspect 4:3 target_file.mp4

Take target_file.mp4 and import into iTunes, then sync with your device. 

=====Generic Bash=====
====Redirecting STDERR to a pipe in Bourne/BASH====

Passing *both* stdout and stderr to the pipe.

  <command> 2>&1 | <command2>

Passing only stderr to the pipe:

  exec 3>&1
  <command> 2>&1 >&3 3>&- | <command2> 3>&-
  exec 3>&- 

=====Backups=====
====Running remote backups to tape with tar====

Use the following command to dump a directory structure to a remote tape drive:
  tar cv --rmt-command=/sbin/rmt --rsh-command /usr/bin/ssh -f <remote_host>:/dev/st0 --directory /path/to/source/dir --label "Label for backup" <directory_name>

Use the following command to recover a directory structure from a remote tape drive:
  tar xv --rmt-command=/sbin/rmt --rsh-command /usr/bin/ssh -f <remote_host>:/dev/st0

Of course, as always with the tar command, one can specify the files/sub-directories to be recovered if one wishes. 



==== rsync usage ====
  
Proper, recursive directory structure copy that preserves permissions, etc.  Also can restart partial transfers, just execute the command again after a failure.

  $ rsync --partial --append --verbose --stats --progress --compress --rsh=/usr/bin/ssh --recursive --times --perms --links <src> <dst>


===== Generic sysadmin stuff =====

====Shutting down the monitor====

  /usr/bin/xset dpms force off

====Mounting a SMB fileshare====

To mount a Windows or Samba SMB fileshare:

  mount -t cifs //ntserver/download -o username=user,password=myPassword /mnt/ntserver


==== top pipline for quick system state ====

Tweak the $8 == 'D' to look at different states of processes.

  top -b -n 1 | awk '{if (NR <=7) print; else if ($8 == "D") {print; count++} } END {print "Total status D: "count}'

Example output

  top - 11:33:29 up 8 days, 18:00,  2 users,  load average: 5.61, 5.35, 7.00
  Tasks: 101 total,   1 running, 100 sleeping,   0 stopped,   0 zombie
  Cpu(s):  2.7%us,  1.9%sy,  0.0%ni, 78.0%id, 16.7%wa,  0.2%hi,  0.5%si,  0.0%st
  Mem:   1991292k total,  1975248k used,    16044k free,    56836k buffers
  Swap:  1150724k total,       36k used,  1150688k free,  1652024k cached
  
    PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND            
    334 root      20   0     0    0    0 D  0.0  0.0   5:16.26 kdmflush           
    959 root      20   0     0    0    0 D  0.0  0.0   4:35.89 jbd2/dm-2-8        
   1080 root      20   0     0    0    0 D  0.0  0.0   1:53.47 nfsd               
   1081 root      20   0     0    0    0 D  0.0  0.0   1:58.73 nfsd               
   1082 root      20   0     0    0    0 D  0.0  0.0   1:52.42 nfsd               
   1083 root      20   0     0    0    0 D  0.0  0.0   1:51.43 nfsd               
   1084 root      20   0     0    0    0 D  0.0  0.0   1:58.40 nfsd               
   1085 root      20   0     0    0    0 D  0.0  0.0   1:50.55 nfsd               
   1086 root      20   0     0    0    0 D  0.0  0.0   1:51.28 nfsd               
   1087 root      20   0     0    0    0 D  0.0  0.0   1:58.37 nfsd               
  Total status D: 10

==== rsyslog - remote host log containment ====

Place at the top of the /etc/rsyslog.d/50-default.conf
 
  :source, isequal, "router_address" /var/log/<log_file_name>
  & ~

===== Networking =====

==== ASN lookup via whois ====

  $ whois -h v4.whois.cymru.com " -c -p 61.0.0.70"
  
  AS | IP | BGP Prefix | CC | AS Name
  9829 | 61.0.0.70 | 61.0.0.0/20 | IN | BSNL-NIB National Internet Backbone

==== Routing ====

=== Checking ===

  cat /proc/sys/net/ipv4/ip_forward

or

  sysctl net.ipv4.ip_forward

=== Enabling ===

On the fly:

  sysctl -w net.ipv4.ip_forward=1

To make it permanent, add the following to /etc/sysctl.conf:
  net.ipv4.ip_forward = 1

Run the following command:
  # sysctl -p /etc/sysctl.conf

==== pcap analysis ====

Wireshark CLI packet analyzer:  tshark

Example for processing Cisco netflow:
  tshark -r test.pcap -n -d udp.port==3010,cflow  -V

===== X-windows Tricks =====

==== Open Remote Desktop Environments ====

Open a second X-windows server on the local host
  xinit -- :1

In the xterm of the resulting desktop on the local host, SSH to the remote host
  ssh -X user@remotehost

In the SSH session to the remote host, start gnome
  gnome-session

Additional X-windows servers can be started on the local host with successive xinit commands using :2, :3, etc.

Alternative desktop environments such as KDE can be used if desired.

==== Changing the primary monitor ====

Check to see the names of the attached outputs:
  xrandr --prop|egrep "VGA|DVI"

Set the one desired:
  xrandr --output DVI-0 --primary