remove old kernels except loaded kernel

remove old kernels on CentOS 8 except loaded kernel

dnf remove --oldinstallonly --setopt installonly_limit=2 kernel

remove old kernels on CentOS 7 except loaded kernel

package-cleanup --oldkernels --count=1

audible ping

using ping

while sleep 3;do ping -a -c 1 8.8.8.8; done

using beep

while sleep 3;do ping -c 1 8.8.8.8 && beep; done

using mplayer

while sleep 3;do ping -c 1 8.8.8.8 && mplayer file.mp3; done

creating columns bash

create 1 column

seq 10

create 2 columns

printf %s\\n ID-{1..3}' '{10..25..5}

create 3 columns

printf %s\\n ID-{1..3}' '{a,b,c}' '{10..20..5}

create 4 or more columns

seq 12 | pr -4t | column -t

delete line match more one before/after with sed

delete line match and one before

echo a b c | tr ' ' "\n" | sed -s 'N;/b/!P;D'

delete line match and one after

echo a b c | tr ' ' "\n" | sed '/b/,+1d'

put char on position X with sed

put space on position 5

echo 1234567 | sed 's/./& /5'

put . on position 5

echo 1234567 | sed 's/./&./5'

how old is your linux installation

tune2fs -l $( df -h | awk '$NF ~ "/$" {print $1}' ) | grep created

search and replace pattern on specific column

using gsub – replace on second column localhost per bar

awk '{ gsub( "localhost","bar",$2 ) }1' /etc/hosts

using ternary operator – if column two is equal localhost replace it per bar

awk '{ $2 = $2=="localhost" ? "bar" : $2 }'1 /etc/hosts