# Linux - Bag of Tricks (Part 2): Certificates, Databases, Disks & Boot
This page continues [Linux - Bag of Tricks](https://docs.thehomestack.io/books/linux/page/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:
```shell
openssl req -nodes -newkey rsa:2048 -keyout privatekey.key -out mail.csr
```
Then, generate a signing request
```shell
openssl x509 -req -days 365 -in mail.csr -signkey privatekey.key -out secure.crt
```
Create a localhost cert on the server
```shell
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
```shell
sudo nmap -sT -p- example.com
```
UDP
```shell
sudo nmap -sU -p- example.com
```
Look for open Ports
```bash
nc -vz 203.0.113.10 514
```
Trace route
```bash
sudo tracepath 203.0.113.10
```
Looking at the Journal, this is an example to look at the mariadb process
```bash
journalctl -u mariadb -f
```
Search in sub folders
```bash
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
```bash
find . -type f -name "KIDSENV" -exec sed -i.bak 's/^KWSQL_LOG=query/#KWSQL_LOG=query/' {} +
```
Delete file on the server
```bash
find . -type f \( -name "SQLQRY*" -o -name "SQLINFO" -o -name "SQLERROR" \) -delete
```
Delete files over 100M
```bash
find . -type f -size +100M
```
Delete files over 100M and list them
```bash
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
```bash
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
```