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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 -rni ~ -e "PENALTY"

➡️ List what hosts are active on the local network:

					arp-scan -l
nmap -sn

➡️ 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

On Linux run:

					# one time, if needed:
# source /opt/intel/oneapi/
/opt/ansys_inc/v221/ansys/bin/ansys221 -b -i mcal_simulation.inp -o log -job job -np 1

➡️ 3 Ways to run LS-DYNA from a terminal:

					lsdyna i=file.k jobid=tmp ncpu=4
/opt/PolymerFEM/PolyUMod/PolyUMod_LSDYNA/lsdyna_dp.e i=mcal_simulation.k jobid=slask
source /opt/intel/oneapi/
mpirun -np 1 /opt/PolymerFEM/PolyUMod/PolyUMod_LSDYNA/lsdyna_dp_mpp.e i=mcal_simulation.k jobId=slask


➡️ 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:






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
dsim = DataFrame(CSV.File("", 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)")

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

➡️ Start zsh command in the background and then disown it:

					sleep 1 &!

➡️ Compress a folder to xz-format:

					tar caf folder.tar.xz folder

➡️ Start another FE simulation on a Linux computer as soon as first FE simulation finishes:

					watch -g ps -opid -p 1714392 ; abq2023 -cpus 36 -job newModel.inp

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


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