Archive for the ‘ Bash ’ Category

Top 25 Best Linux Commands

Top 25 Best Linux Commands.

25) sshfs name@server:/path/to/folder /path/to/mount/point
Mount folder/filesystem through SSH
Install SSHFS from http://fuse.sourceforge.net/sshfs.html
Will allow you to mount a folder security over a network.

24) !!:gs/foo/bar
Runs previous command replacing foo by bar every time that foo appears
Very useful for rerunning a long command changing some arguments globally.
As opposed to ^foo^bar, which only replaces the first occurrence of foo, this one changes every occurrence.

23) mount | column -t
currently mounted filesystems in nice layout
Particularly useful if you’re mounting different drives, using the following command will allow you to see all the filesystems currently mounted on your computer and their respective specs with the added benefit of nice formatting.

22) <space>command
Execute a command without saving it in the history
Prepending one or more spaces to your command won’t be saved in history.
Useful for pr0n or passwords on the commandline.

21) ssh user@host cat /path/to/remotefile | diff /path/to/localfile –
Compare a remote file with a local file
Useful for checking if there are differences between local and remote files.

20) mount -t tmpfs tmpfs /mnt -o size=1024m
Mount a temporary ram partition
Makes a partition in ram which is useful if you need a temporary working space as read/write access is fast.
Be aware that anything saved in this partition will be gone after your computer is turned off.

19) dig +short txt <keyword>.wp.dg.cx
Query Wikipedia via console over DNS
Query Wikipedia by issuing a DNS query for a TXT record. The TXT record will also include a short URL to the complete corresponding Wikipedia entry.

18) netstat -tlnp
Lists all listening ports together with the PID of the associated process
The PID will only be printed if you’re holding a root equivalent ID.

17) dd if=/dev/dsp | ssh -c arcfour -C username@host dd of=/dev/dsp
output your microphone to a remote computer’s speaker
This will output the sound from your microphone port to the ssh target computer’s speaker port. The sound quality is very bad, so you will hear a lot of hissing.

16) echo “ls -l” | at midnight
Execute a command at a given time
This is an alternative to cron which allows a one-off task to be scheduled for a certain time.

15) curl -u user:pass -d status=”Tweeting from the shell” http://twitter.com/statuses/update.xml
Update twitter via curl

14) ssh -N -L2001:localhost:80 somemachine
start a tunnel from some machine’s port 80 to your local post 2001
now you can acces the website by going to http://localhost:2001/

13) reset
Salvage a borked terminal
If you bork your terminal by sending binary data to STDOUT or similar, you can get your terminal back using this command rather than killing and restarting the session. Note that you often won’t be able to see the characters as you type them.

12) ffmpeg -f x11grab -s wxga -r 25 -i :0.0 -sameq /tmp/out.mpg
Capture video of a linux desktop

11) > file.txt
Empty a file
For when you want to flush all content from a file without removing it (hat-tip to Marc Kilgus).

10) $ssh-copy-id user@host
Copy ssh keys to user@host to enable password-less ssh logins.
To generate the keys use the command ssh-keygen

9) ctrl-x e
Rapidly invoke an editor to write a long, complex, or tricky command
Next time you are using your shell, try typing ctrl-x e (that is holding control key press x and then e). The shell will take what you’ve written on the command line thus far and paste it into the editor specified by $EDITOR. Then you can edit at leisure using all the powerful macros and commands of vi, emacs, nano, or whatever.

8 ) !whatever:p
Check command history, but avoid running it
!whatever will search your command history and execute the first command that matches ‘whatever’. If you don’t feel safe doing this put :p on the end to print without executing. Recommended when running as superuser.

7) mtr google.com
mtr, better than traceroute and ping combined
mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.
As mtr starts, it investigates the network connection between the host mtr runs on and HOSTNAME. by sending packets with purposly low TTLs. It continues to send packets with low TTL, noting the response time of the intervening routers. This allows mtr to print the response percentage and response times of the internet route to HOSTNAME. A sudden increase in packetloss or response time is often an indication of a bad (or simply over‐loaded) link.

6 ) cp filename{,.bak}
quickly backup or copy a file with bash

5) ^foo^bar
Runs previous command but replacing
Really useful for when you have a typo in a previous command. Also, arguments default to empty so if you accidentally run:
echo “no typozs”
you can correct it with
^z

4) cd –
change to the previous working directory

3):w !sudo tee %
Save a file you edited in vim without the needed permissions
I often forget to sudo before editing a file I don’t have write permissions on. When you come to save that file and get the infamous “E212: Can’t open file for writing”, just issue that vim command in order to save the file without the need to save it to a temp file and then copy it back again.

2) python -m SimpleHTTPServer
Serve current directory tree at http://$HOSTNAME:8000/

1) sudo !!
Run the last command as root
Useful when you forget to use sudo for a command. “!!” grabs the last run command.

Avoid race condition for file creation

race condition in the common lock on file? – Stack Overflow.

A possible solution to this is to use IO redirection and bash’s noclobber mode, which won’t redirect to an existing file. We can use something similar to:

if ( set -o noclobber; echo "$$" > "$lockfile") 2> /dev/null;
then
   # BK: this will cause the lock file to be deleted in case of other exit
   trap 'rm -f "$lockfile"; exit $?' INT TERM EXIT

   # critical-section BK: (the protected bit)

   rm -f "$lockfile"
   trap - INT TERM EXIT
else
   echo "Failed to acquire lockfile: $lockfile."
   echo "Held by $(cat $lockfile)"
fi

Disk I/O stats from /proc/diskstats

Disk I/O stats from /proc/diskstats

cat /proc/diskstats | grep 'sda '
   8    0 sda 2461810 61427 148062742 6482992 660009 1544934 67900384 45642376 0 7162961 52128751

Field 1 — # of reads issued
Field 2 — # of reads merged, field 6 — # of writes merged
Field 3 — # of sectors read
Field 4 — # of milliseconds spent reading
Field 5 — # of writes completed
Field 7 — # of sectors written
Field 8 — # of milliseconds spent writing
Field 9 — # of I/Os currently in progress
Field 10 — # of milliseconds spent doing I/Os
Field 11 — weighted # of milliseconds spent doing I/Os