Linux Tips and Tricks

Here is a collection of Linux commands and hints 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 ncpu=4
				
			

➡️ 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
				
			

➡️ 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
				
			

➡️ Neo-Hookean:

				
					C10 = mu / 2
mu = 2 C10
				
			

➡️ Read in and plot data using Julia

				
					using Plots, CSV, DataFrames
pyplot()

dsim = DataFrame(CSV.File("file.data", delim=' ', ignorerepeated=true))
plot!(dsim[:,1], dsim[:,2], label="FEA", linestyle=:dash, linewidth=2)

plot!(size=(1200,800), xlims=(12.0, 20.0), ylims=(0.0, 60.0), legend=:topright, framestyle=:box)
plot!(tickfontsize=14, guidefontsize=16, legendfontsize=10, xlabel="Displacement", ylabel="Radial Force (N)")

savefig("fig.png")

				
			
				
					using Plots
pyplot()
x = range(1, 100, length=50)
y = 2.0 .* x.^3.5
plot(x, y, xaxis=:log, yaxis=:log)
				
			

In the comments below, indicate if you have any other “tricky” commands that you would like to add!

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