Linux Tips and Tricks

Introduction

Here is a collection of Linux commands that I find useful:

• Search for all inp-files that contain the text “PENALTY” (case insensitive)

  grep --include=\*.inp -rnwli ~ -e "PENALTY"

• List what hosts are active on the local network:

  arp-scan -l
  nmap -sn 192.168.86.0/24

• Debugging a core dump:

  gdb executable core
  thread apply all bt

• To determine if a Redhat / CentOS computer needs to be rebooted:

  sudo needs-restarting -r

• Enable core dumps on Redhat / CentOS. As root type (needs to be done after each reboot):

  echo /tmp/core-%e-sig%s-user%u-group%g-pid%p-time%t > /proc/sys/kernel/core_pattern

• Split and combine HUGE files:

  split --verbose -b1G file.tar file.tar.
  cat file.tar.* > file.tar

• Update PolyUMod and MCalibration files (the \ before cp runs the command without any alias):

  cd PolyUMod_Installer_Lin64_vX.X.X/files
  \cp -r -p * /opt/PolymerFEM/

• Run ANSYS in batch mode from a Windows PowerShell:

  C:/"Program Files"/"ANSYS Inc"/v192/ansys/bin/winx64/ANSYS192.exe -b -i simulation.dat -o job.output -j job -dis -np 1

• Run LS-DYNA from a terminal:

  lsdyna i=file.k jobid=tmp

• Create an animated gif-image from a set of png-images:

  convert -delay 150 -loop 0 *png myimage.gif

• Setup vim so that only tabs with a width of 4 are used:

  set autoindent noexpandtab tabstop=4 shiftwidth=4

• Take a screen shot of a region in Ubuntu 20.04:

  Ctrl + Shift + Print

• Run a Windows installer in debug mode (I know, this is not for Linux, but still useful):

  msiexec /i Installer.msi /L*V C:\Temp\log.txt

• When I tried to ANSYS v201 on Ubuntu 20.04 I got error like the following

  Syntax error: Bad fd number

  I was able to fix that odd error by editing the first line of the following 3 files:

  /opt/ansys_inc/v201/ansys/bin/ansysdis
  /opt/ansys_inc/v201/ansys/bin/mapdl
  /opt/ansys_inc/v201/ansys/bin/anssh.ini

  from

  #!/bin/sh

  to

  #!/bin/bash

  Now I can run the latest version of ANSYS on the latest version of Ubuntu. Cool.
• Convert many 12-bit tif images to 16-bit images:

  for a in *tif; convert $a -depth 16 new_$a 

In the comments below, indicate what important (and “tricky”) commands that you would like to add!