Nethogs is a useful tool for monitor bandwidth consumption by pid. Tested on Debian an CentOs
:q to quit
-l outputs only the file names -i ignores the case -r descends into subdirectories
Useful when you've produced a large file of numbers, and want to quickly see the distribution. The value of y halfway along the x axis is the median. Simple! Just create the listOfNumbers.txt file with a number on each line to try it out.
This will perform one of two blocks of code, depending on the condition of the first. Essentially is a bash terniary operator.
To tell if a machine is up:
ping -c1 machine { echo succes;} || { echo failed; }
Because of the bash { } block operators, you can have multiple commands
ping -c1 machine && { echo success;log-timestamp.sh }|| { echo failed; email-admin.sh; }
Tips:
Remember, the { } operators are treated by bash as a reserved word: as such, they need a space on either side.
If you have a command that can fail at the end of the true block, consider ending said block with 'false' to prevent accidental execution
Show Sample Output
It can resume a failed secure copy ( usefull when you transfer big files like db dumps through vpn ) using rsync. It requires rsync installed in both hosts. rsync --partial --progress --rsh=ssh $file_source $user@$host:$destination_file local -> remote or rsync --partial --progress --rsh=ssh $user@$host:$remote_file $destination_file remote -> local
Using process substitution, we can 'trick' tee into sending a command's STDOUT to an arbitrary number of commands. The last command (command4) in this example will get its input from the pipe. Show Sample Output
This is shorter and actually much faster than >/dev/null (see sample output for timings) Plus, it looks like a disappointed face emoticon. Show Sample Output
Instead of deleting an existing symlink and then re-creating it pointing at the new location, it is possible to perform the same action with this one command. Interesting discussion on whether this is possible to do atomically here: http://answers.google.com/answers/threadview?id=526119
This command 1. SSH into a machine 2. Tunnels VNC port to your local computer ("-L 5900:localhost:5900") 3. Runs a single use vnc server ("x11vnc -safer -localhost -nopw -once -display :0") 4. Goes into the background ("-f") 5. Runs VNC viewer on the local computer connecting to the remote machine via the newly created SSH tunnel ("vinagre localhost:5900")
~ is the ssh control character. If you type it after a newline, you can example force close the ssh session. , ~, then . If you want more info, type ~? when you are connecting using ssh. Very useful to kill of any hanging ssh sessions when nothing else works.
awk is evil! Show Sample Output
The simplest way I know. Show Sample Output
This has helped me numerous times trying to find either log files or tmp files that get created after execution of a command. And really eye opening as to how active a given process really is. Play around with -anewer, -cnewer & -newerXY Show Sample Output
In turn you can get the contents of your clipboard by typing xsel by itself with no arguments:
xsel
This command requires you to install the xsel utility which is free
With: -vcodec, you choose what video codec the new file should be encoded with. Run ffmpeg -formats E to list all available video and audio encoders and file formats. copy, you choose the video encoder that just copies the file. -acodec, you choose what audio codec the new file should be encoded with. copy, you choose the audio encoder that just copies the file. -i originalfile, you provide the filename of the original file to ffmpeg -ss 00:01:30, you choose the starting time on the original file in this case 1 min and 30 seconds into the film -t 0:0:20, you choose the length of the new film newfile, you choose the name of the file created. Here is more information of how to use ffmpeg: http://www.ffmpeg.org/ffmpeg-doc.html
This uses awk to grab the IP address from each request and then sorts and summarises the top 10.
We all know...
nice -n19
for low CPU priority.
ionice -c3
for low I/O priority.
nocache can be useful in related scenarios, when we operate on very large files just a single time, e.g. a backup job. It advises the kernel that no caching is required for the involved files, so our current file cache is not erased, potentially decreasing performance on other, more typical file I/O, e.g. on a desktop.
http://askubuntu.com/questions/122857
https://github.com/Feh/nocache
http://packages.debian.org/search?keywords=nocache
http://packages.ubuntu.com/search?keywords=nocache
To undo caching of a single file in hindsight, you can do
cachedel <OneSingleFile>
To check the cache status of a file, do
cachestats <OneSingleFile>
Needed a quick way to see if my server distro that I setup years ago was running 32bit or not, since with time I had forgotten. Note: does not check _hardware_ e.g. /proc/cpuinfo but rather the kernel installed Show Sample Output
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