linux-cheat-sheet

Delete open files. When df and du show different results.

find /proc/*/fd -ls | grep '(deleted)' | awk '{print $11}' | xargs -I % sh -c 'echo /dev/null > %'

Du with excludes.

du --exclude=/d0 --exclude=/d1 -hd 1 /

Cron syntax.

*     *     *   *    *       user   command_to_execute
|     |     |   |    |
|     |     |   |    |
|     |     |   |    +----- day of the week (0 - 7) [both 0 and 7 represent Sunday]
|     |     |   +------- month (1 - 12)
|     |     +--------- day of the month (1 - 31)
|     +----------- hour (0 - 23)
+------------- minute (0 - 59)

Every 5 min
*/5 * * * * user command_to_execute

Every hour, from 9:00 to 18:00
00 09-18 * * * user command_to_execute

Every day, at 9:00 and 18:00
00 09,18 * * * user command_to_execute

Every day, at 17:30
30 17 * * * user command_to_execute

Every weekday, at 17:30
30 17 * * Mon,Tue,Wed,Thu,Fri user command_to_execute

Find, Search by directory name.

find . -type d -name '*text.txt'

Find, Search by last modified.

find . -type f -printf '%TY-%Tm-%Td %TT %p\n' | sort -r

Grep, Regular expression to search for text in files.

grep -rni -E '^text' .

Checking the ssl certificate.

openssl x509 -in /dir/ca.crt -text -noout

My bash prompt (PS1).

#vim .bashrc

#########################################################################

timer_start() {
  timer=${timer:-$SECONDS}
}
timer_stop() {
  timer_show=$(($SECONDS - $timer))
  unset timer
}
trap 'timer_start' DEBUG
if [ "$PROMPT_COMMAND" == "" ]; then
  PROMPT_COMMAND="timer_stop"
else
  PROMPT_COMMAND="$PROMPT_COMMAND; timer_stop"
fi

# https://github.com/jonmosco/kube-ps1
#Ubuntu
#source /home/pbujakiewicz/.kube-ps1/kube-ps1.sh
#MacOS
source "/opt/homebrew/opt/kube-ps1/share/kube-ps1.sh"
KUBE_PS1_SYMBOL_COLOR='cyan'
KUBE_PS1_CTX_COLOR='green'
KUBE_PS1_NS_ENABLE='false'
KUBE_PS1_PREFIX='['
KUBE_PS1_SUFFIX=']'

parse_git_branch() {
  git branch 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/\1/'
}

if [ "$color_prompt" = yes ]; then
  PS1='\n[\[\033[01;32m\]\D{%H:%M:%S}\[\033[00m\]]\[\e[m\] [\[\033[01;36m\]\w\[\033[00m\]] [\[\033[01;32m\]$(parse_git_branch)\[\033[00m\]]\[\e[m\] [${timer_show}s]\n$(kube_ps1)\n\[\033[01;32m\]\$\[\033[00m\]\[\e[m\] '
else
  PS1='\n[D{%H:%M:%S}] [\w] [$(parse_git_branch)] [${timer_show}s]\n$(kube_ps1)\n\$ '
fi

#########################################################################

Git rebase master on branch.

git fetch
git rebase origin/master

LDAP search.

No TLS
ldapsearch -x -H "ldap://127.0.0.1:389" -D "CN=ldap auth,OU=SA,DC=company,DC=com" -w password -b "OU=Search here,DC=company,DC=com" "(&(objectClass=group)(|(cn=dev*)(cn=devops*)))"

TLS
env LDAPTLS_CACERT=domain.cer ldapsearch -x -H "ldaps://127.0.0.1:389" -D "CN=ldap auth,OU=SA,DC=company,DC=com" -w password -b "OU=Search here,DC=company,DC=com" "(&(objectClass=group)(|(cn=dev*)(cn=devops*)))"

or graphical solution
Apache Directory Studio - https://directory.apache.org/studio/

LVM Resize.

# scan pci for new disk
find /sys -iname 'scan'
echo "- - -" > /sys/devices/pci0000:00/0000:00:07.1/host0/scsi_host/host0/scan

# scan resize old disk
echo 1>/sys/class/block/sdX/device/rescan

# create PV and add to group
pvcreate /dev/sda
sudo vgextend centos /dev/sda

# scan when PV is whole disk and is added to group
pvresize /dev/sda

# add 10 GB
lvextend -L+10G /dev/mapper/vol

# add 100% free space
lvextend -l+100%FREE /dev/mapper/vol

# xfs file system
xfs_growfs /dev/centos/var

# ext3/4 file system
resize2fs /dev/centos/var

innodb_buffer_pool_size mysql

# go root
sudo su -

#checking current values
grep 'innodb_buffer_pool_size' /etc/my.cnf
echo "SHOW GLOBAL VARIABLES LIKE 'innodb_buffer_pool_size';" | mysql
echo "SELECT ROUND (@@innodb_buffer_pool_size / 1024 / 1024 / 1024, 2) 'innodb_buffer_pool_size (GB)';" | mysql

#recalculation
echo $((307 * 1024 * 1024 * 1024))
echo $((329638739968 / 1024 / 1024 / 1024))

#change
#mysql sometimes does not accept the <NEW_SIZE>, then you have to decrease it!!
echo "SET GLOBAL innodb_buffer_pool_size=<NEW_SIZE>;" | mysql
#file
vim /etc/my.cnf

Mysql - find and kill process by IP

SELECT ID,HOST,DB,COMMAND,TIME,STATE,INFO FROM information_schema.processlist WHERE HOST LIKE '10.10.10.10%' ORDER BY TIME DESC;

KILL 0001;

Find IP in NewRelic.

SELECT uniques(host.ipV4Address) FROM Metric WHERE host.hostname LIKE '%jenkins-test%' AND host.ipV4Address IS NOT NULL

Loop in bash terminal.

# for loop
for i in {1..5}; do echo "Liczba: $i"; done
for file in $(ls /home/pbujakiewicz/); do echo "Plik: $file"; done

# while loop
while true; do echo "To się powtarza"; sleep 1; done

Mounting NFS and CIFS.

# NFS
sudo mount -t nfs <server_ip>:/path/to/share /local/mount/point
sudo umount /local/mount/point

#/etc/fstab
<server_ip>:/path/to/share /local/mount/point nfs defaults 0 0

# CIFS
sudo mount -t cifs -o username=<user>,password=<password> //<server_ip>/<share_name> /local/mount/point
sudo umount /local/mount/point

#/etc/fstab
//<server_ip>/<share_name> /local/mount/point cifs username=<user>,password=<password> 0 0
//<server_ip>/<share_name> /local/mount/point cifs credentials=/etc/cifs-credentials 0 0

Copying a directory via ssh. Useful when no space on device.

rsync -vaz -e ssh /home/devops/dir devops@10.0.0.1:/home/devops/.
or
tar czpf - /home/devops/dir | ssh devops@10.0.0.1 "sudo tar xzpf - --strip-components=2 -C /home/devops"

nohup, an alternative when screen is not installed.

# start
cd /tmp/
nohup tar czpf - /home/devops/dir | ssh devops@10.0.0.1 "sudo tar xzpf - --strip-components=2 -C /home/devops" 2>&1 &

# check
ps aux | grep tar

# stop
kill 12345

screen.

# install
sudo apt install screen
sudo yum install screen

# check
screen -ls

# start
screen -S file

# detach a screen session
screen -d 1234
# or
Ctrl + a + d

# reattach a screen session
screen -r 1234

# stop
exit

Akamai staging one line test - cache.

curl -sSI --resolve web.bujakiewiczpawel.pl:443:$(dig +short web.bujakiewiczpawel.pl.edgekey-staging.net | tail -1) https://web.bujakiewiczpawel.pl/api/XXX/home | grep -i cache-control