BASH

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Using BASH command Find to locate files – Part 1

Use command to list files in the lammps-7Aug19 directory

[u1@node1 lammps-7Aug19]$ find

Count the number of files by piping the list to wc to count the files.

[u1@node1 lammps-7Aug19]$ find | wc -l
14717

Count the the directories listing by piping the list to wc to count the directories

[u1@node1 lammps-7Aug19]$ find -type d | wc -l
672

Count the list of files that matched the wildcard pattern *.mov that are larger than 1M by piping to wc to count

[u1@node1 lammps-7Aug19]$ find -type f -name "*.jpg" -size +1M |wc -l

Find and match files or directories whose contents or attributes were last modified more recently than those of “mybasefile”

[u1@node1 lammps-7Aug19]$ find -type f -name "*.jpg" -cnewer mybasefile

Find empty files in the lammps-7Aug19 directory

[u1@node1 lammps-7Aug19]$ find -type f -empty

Find files or directories that belongs to username

[u1@node1 Downloads]$ find -type f -user root |wc -l
1572

References:

  1. The Linux Command Line
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Checking and Modifying Timestamp of whole Directory recursively

Step 1: Show the complete date, time and year for a specific file

$ ls -l --full-time
-rwxrwxr-x  1 root root  1109 2018-07-20 12:52:52.587945000 +0800 Allwmake
drwxrwxr-x  5 root root  4096 2018-07-20 12:52:52.602945000 +0800 applications
drwxrwxr-x  3 root root  8192 2018-07-20 12:53:19.536973000 +0800 bin
-rw-rw-r--  1 root root 35646 2018-07-20 12:52:52.592945000 +0800 COPYING
drwxrwxr-x  5 root root  4096 2018-07-20 12:53:19.936974000 +0800 doc
drwxrwxr-x  8 root root  4096 2018-07-20 12:53:20.039974000 +0800 etc
drwxr-xr-x  4 root root  4096 2018-07-20 12:55:17.230101000 +0800 platforms
-rw-rw-r--  1 root root  1620 2018-07-20 12:52:52.597945000 +0800 README.org
drwxrwxr-x 38 root root  4096 2018-07-20 12:53:22.032976000 +0800 src
drwxrwxr-x 17 root root  4096 2018-07-20 12:54:45.114064000 +0800 tutorials
drwxrwxr-x  7 root root  4096 2018-07-20 12:55:15.939099000 +0800 wmake

Step 2: If you wish to modify the time-stamp for the entire directory, you can use the command,

% for file in `find .`; do touch $file; done

References:

  1. touch – change file timestamps(Unix Tutorial)
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Quick and Dirty way to ensure only one instance of a shell script is running at a time

This script is taken from Quick and Dirty way to ensure only one instance of a shell script is running at a time

For example, this can be used to ensure SAGE Mirroring rsync run once.

# rsyncs from sage.math.washington.edu using its rsync daemon
# for automated use, remove the "vv" and "progress" switches

# locking mechanism from
# http://stackoverflow.com/questions/185451/quick-and-dirty-way-to-ensure-only-one-instance-of-a-shell-script-is-running-at-a

LOCKFILE=./rsync_sagemath.lock

if [ -e ${LOCKFILE} ] && kill -0 `cat ${LOCKFILE}`; then
echo "rsync_sagemath already running ... exit"
exit
fi

# make sure the lockfile is removed when we exit and then claim it
trap "rm -f ${LOCKFILE}; exit" INT TERM EXIT
echo $ > ${LOCKFILE}

rsync -av --delete-after rsync.sagemath.org::sage /var/www/html/sage

rm -f ${LOCKFILE}
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Simple BASH script to setup shared SSH keys on Cluster

Here is my simple script to setup shared SSH keys on Cluster. You can put this script called ssh-shared-keys.sh into /etc/skel/.bash_profile so that the new users have their keys shared between all the compute nodes.

#!/bin/bash

# Exit script on Error
set -e

# Check for SSH Directory
if [ ! -d ~/.ssh ]; then
   mkdir -p ~/.ssh/
fi


# Check for existence of passphrase
if [ ! -f ~/.ssh/id_rsa.pub ]; then
        ssh-keygen -t rsa -N "" -f ~/.ssh/id_rsa
        echo "Execute ssh-keygen --[done]"
fi

# Check for existence of authorized_keys and append the shared ssh keys
if [ ! -f ~/.ssh/authorized_keys ]; then
        touch ~/.ssh/authorized_keys
        echo "Create ~/.ssh/authorized_keys --[done]"
        chmod 700 ~/.ssh/authorized_keys
        cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
        echo "Append the public keys id_rsa into authorized keys --[done]"
        chmod 400 ~/.ssh/authorized_keys
        chmod 700 ~/.ssh/
fi

# Create user's ssh config it not exist
if [ ! -f ~/.ssh/config ]; then
        touch ~/.ssh/config
        echo "StrictHostKeyChecking no" > ~/.ssh/config
        echo "StrictHostKeyChecking no --[done]"
        chmod 644 ~/.ssh/config
fi
# Unset error on exit or it will affect after bash command :)
set +e

References:

  1. Helping users to SSH without password into the Compute Nodes manually
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Using the command “ls” options and arguments

ls has some interesting format which is very useful. Here are some arguments which you can use. For example, I like

$ ls - ltF
 -a   –all  All files include those with .
 -l  Display results in long format
 -r   –reverse  Reverse order while sorting
 -S  Sort results by file size
 -t  Sort by modification time.
 -F   –classify  Append an indicator character to the end of each listed name

References:

  1. The Linux Command Line (by No Starch Press)