Skip to main content

nohup command in Linux

Often you come across a situation where you try to open a machine remotely using ssh and try to start a server or a run a command indefinitely.

But once you close the ssh session, your session also terminates and the background process also terminates. So here is a solution.

To open ssh remotely,

prompt $] ssh username@machinename
Ex: ssh root@
Ex: ssh 
prompt $] ssh -X username @machinename 
Ex. ssh -X root@ 

(this -X indicates the remote session can be opened in X window (GUI) mode)

Assume we need to start a httpd server in the remote machine.
we can issue the command like this

prompt$] nohup command 
if any error or log information may be stored in the nohup.out file. if you want to redirect to a file use the redirected symbol (1>  indicates standard output and 2> indicates standard Error). Specify the filenames for the output. Here is the typical nohup command to start the httpd server.

prompt $] nohup  /etc/init.d/httpd start  1> file.out 2> file.err & 
nohup is the command simply tells "no hangup". This will send the output to non-tty.
The above command will start the httpd server and any error or output will be written on to the files file.err and file.out respectively (The & indicates the background process that closes the current terminal and prompts for further inputs).
nohup in Linux

This command I learnt when i try to deploy Sage math libraries in a IBM Blade Server. We were really struggling to run the notebook in sagemath library. But finally accomplished using the nohup command.

The alternative to nohup is crontab or cronjob can be used.

 T S Pradeep Kumar


Popular posts from this blog

AWK Scripts for NS2 to process data from Trace Files

AWK Scripts are very good in processing the data from the log (trace files) which we get from NS2. If you want to process the trace file manually, here is the detailHere is a sample of trace file from NS2 (However ns2 supports a new type of trace file also), but this post will make you understand the old trace format only.r 0.030085562 _0_ MAC  --- 0 message 32 [0 ffffffff 1 800] ------- [1:255 -1:255 32 0] r 0.030110562 _0_ RTR  --- 0 message 32 [0 ffffffff 1 800] ------- [1:255 -1:255 32 0] s 1.119926192 _0_ RTR  --- 1 message 32 [0 0 0 0] ------- [0:255 -1:255 32 0]
AWK Scripts are very good in processing the data column wise. For example
the first column in the above trace file represents r, s which indicates receive, sent respectively. If we want to trace the entire r and s alone from this trace file we can represent it as $1
$1 represents ACTION
$2 Time
$3 Node ID
$4 Layer
$5 Flags
$6 seqno
$7 type
$8 Size
$14 Energy (if the network nodes includes EnergyModel)To run the awk script in Li…

nam installation - Segmentation Fault (Solved)

If you are encountering "Segmentation Fault" error while running nam in Ubuntu 14.04 or Linux Mint 17+ editions, this post will be helpful for you.

Download the nam file from this link

First, remove the nam which was installed earlier using the following command 

pradeep@localhost $] sudo apt-get remove nam

and install the new nam which was downloaded just now. go to the folder where the file was downloaded and issue the following command

pradeep@localhost $]  sudo dpkg --install nam_1.15-10_i386.deb

See the screenshot below to install and use nam

 T S Pradeep Kumar

Installation of ns2 in Ubuntu 18.04 - NS2 Tutorial # 2

ns2 installation in Ubuntu 18.04

Unlike earlier version of ubuntu, the 18,04 version does not support the direct installation of ns2, because of the latest C/C++ compiler (7.x), but the latest C/C++ compiler supported by ns2 is gcc-4.8. So this post and video tells you about the installation of gcc-4.8 version, then ns2 and then configuration.
Here are the steps, Please follow the video given below for more information.

$] tar zxvf ns-allinone-2.35.tar.gz

$] sudo apt install gcc-4.8 g++-4.8

if you have installed ubuntu just now, you can try these commands also in the beginning

$] sudo apt update
$] sudo apt install build-essential autoconf automake libxmu-dev

$] cd ns-allinone-2.35/ns-2.35
$] gedit
$] gedit linkstate/ls.h

line number 137, change erase to this->erase
$] cd ..
$] ./install

export PATH=$PATH:/home/pradeepkumar/ns-allinone-2.35/bin:/home/pradeepkumar/ns-allinone-2.35/tcl8.5.10/unix:/home/pradeepkumar/ns-allinone-2.35/tk8.5.10/unix