Linux - Bag of Tricks (Part 2): Certificates, Databases, Disks & Boot

This page continues Linux - Bag of Tricks.

Create a CERT

First, you need to generate the private key and the Certificate Signing Request (CSR). You can do this via the openssl command:

openssl req -nodes -newkey rsa:2048 -keyout privatekey.key -out mail.csr  

Then, generate a signing request

openssl x509 -req -days 365 -in mail.csr -signkey privatekey.key -out secure.crt

Create a localhost cert on the server

openssl req -newkey rsa:2048 -nodes -keyout /etc/pki/tls/private/localhost.key -x509 -days 365 -out /etc/pki/tls/certs/localhost.crt

Mariadb Log Rotate

If log file is large, try if the logrotate

logrotate --force /etc/logrotate.d/mariadb

MySQL Fail to Start

If MySQL does not restart, it probably will not as the index of the log files will not be changed

cd /var/lib/mysql mv ib_logfile0 ib_logfile0.old mv ib_logfile1 ib_logfile1.old systemctl restart mariadb

 

Configure Rsync

Useful for system migrations

Create a “/etc/rsyncd.conf” containing:

[root]

exclude = /dev /etc/fstab /proc /sys

path = /

read only = yes

list = yes

uid = root

gid = root

 

Enable and start:

systemctl enable rsyncd.service

systemctl start rsyncd.service 

Change Run level

systemctl set-default multi-user.target

To switch from graphical to multi-user:

systemctl isolate multi-user.target;

Change Local settings

# timedatectl set-timezone Europe/London  

# localectl set-locale LANG=en_GB.UTF-8

# localectl set-keymap uk

Temporary change

$ loadkeys us

Configure Alternate Authentication

authconfig-tui

SSD Considerations

Change the value of “issue_discards” option from 0 to 1 in “/etc/lvm/lvm.conf”

# systemctl enable fstrim.timer

Adjust “/etc/fstab”

/dev/mapper/xxx /XXX     xfs     defaults,noatime,discard        0 0

Optionally set /tmp in RAM

# systemctl enable tmp.mount

Adding a Disk

# parted /dev/sdx

 

mklabel gpt

unit s

mkpart primary 2048s 100%

set 1 lvm on

quit

 

# pvcreate /dev/sdx1

# vgcreate rl_ssd /dev/sdx1

# lvcreate –L 50GB -n mysql rl_ssd

# mkfs.xfs /dev/rl-ssd/mysql

# blkid /dev/sdc

# chown mysql:mysql /var/lib/mysql

Growing a lvm partition

# parted /dev/sdc

 

(parted) unit b

(parted) print free

Number  Start        End           Size          Type     File system  Flags

 1      31744B       5368709119B   5368677376B   primary

        5368709120B  21474836479B  16106127360B           Free Space

(parted) resizepart 1  21474836479B

(parted) quit

 

# pvresize /dev/sdc1

 

 

Updating Bootloader configuration

/etc/default/grub

grub2-mkconfig -o /boot/grub2/grub.cfg

NMAP Scan for all Open Ports

TCP

sudo nmap -sT -p- example.com

UDP

sudo nmap -sU -p- example.com

Look for open Ports

nc -vz 203.0.113.10 514

Trace route

sudo tracepath 203.0.113.10

Looking at the Journal, this is an example to look at the mariadb process

journalctl -u mariadb -f

Search in sub folders

grep -r "MYSQL_HOST" . --include="compose.yaml" --include="docker-compose.yml"

Change Lines in KIDSENV and make a backup of it with a .bak extentions

find . -type f -name "KIDSENV" -exec sed -i.bak 's/^KWSQL_LOG=query/#KWSQL_LOG=query/' {} +

Delete file on the server 

find . -type f \( -name "SQLQRY*" -o -name "SQLINFO" -o -name "SQLERROR" \) -delete

Delete files over 100M

find . -type f -size +100M

Delete files over 100M and list them

find . -type f -size +100M -exec ls -lh {} +

Grep files named TX*.DA that are only 1 month back and files lines that have RETDT or RETHD

find . -type f -name "TX*.DA" -mtime -30 -exec grep -iE "RETDT|RETHD" {} +

Remove certain directory

find /path/to/drive/root -type d -name "@eaDir" -print0 | xargs -0 rm -rf