*nix notes

fallocate -l 2G /swapfile

chmod 600 /swapfile

mkswap /swapfile

swapon /swapfile

After this edit /etc/fstab and add swap file to allow it on booting.

add:

Lets say you have RAID1 array created with mdadm and you want to replace disk sdb with new one.

To view raid devices:

cat /prod/mdstat

Then remove associated partitions with md devices:

mdadm /dev/md0 --remove /dev/sdb2 mdadm /dev/md1 --remove /dev/sdb3

If it gives error that it cant be removed, then before removing make them failed:

mdadm /dev/md0 -f /dev/sdb2 mdadm /dev/md1 -f /dev/sdb3

Then insert new disk and copy partitions from working disk sda to new disk sdb:

sfdisk -d /dev/sda | sfdisk /dev/sdb

Then add new drive to arrays:

mdadm /dev/md0 --add /dev/sdb2 mdadm /dev/md1 --add /dev/sdb3

And finally install grub to new disk:

To check certificate type:

openssl x509 -noout -modulus -in cert.crt | openssl md5

To check key:

openssl rsa -noout -modulus -in cert.key | openssl md5

On your server run:

ssh-keygen -t rsa

You will be asked for key location and password, just leave them empty and then keys will be created in home directory of your user, for exmaple:

/root/.ssh

Then we need to copy public key to remote server:

ssh-copy-id -i ~/.ssh/id_rsa.pub user@server

Replace user with user on remote side and server with server address. You will be asked for password of remote server, fill it.

After this you can connect to remote server with command:

If you see in /var/log/messages such errors:

Apr 14 01:53:37 service-1 systemd: Starting MySQL watcher service...

Apr 14 01:53:37 service-1 systemd: Started MySQL watcher service.

Apr 14 01:53:37 service-1 mysqld: 2022-04-14 1:53:37 140260687537920 [Warning] Access denied for user 'admin'@'localhost' (using password: YES)

Apr 14 01:53:37 service-1 mysqld: 2022-04-14 1:53:37 140260688766720 [Warning] Access denied for user 'root'@'localhost' (using password: NO)

Apr 14 01:53:37 service-1 mysqld: 2022-04-14 1:53:37 140260685080320 [Warning] Access denied for user 'root'@'localhost' (using password: NO)

Apr 14 01:53:37 service-1 systemd: db_governor.service: main process exited, code=exited, status=1/FAILURE

Apr 14 01:53:37 service-1 systemd: Unit db_governor.service entered failed state.

Apr 14 01:53:37 service-1 systemd: db_governor.service failed.

Apr 14 01:53:40 service-1 systemd: db_governor.service holdoff time over, scheduling restart.

Apr 14 01:53:40 service-1 systemd: Stopped MySQL watcher service.

Then you have incorrect password of mysql admin user in db governer config. To fix it:

nano /etc/container/mysql-governor.xml

Look for section:

<connector login="admin" password="

There will be encoded password started with $AES

Now we need to get actual password, to do it run:

cat /etc/psa/.psa.shadow

To restart VMware services on host, run this command:

/sbin/services.sh restart

First of all you need to install certbot utility. If you have any webserver runned you must stop it.

Then use command:

certbot certonly -d yourdommain.net

Answer the questions, on How would you like to authenticate with the ACME CA? step choose number 1

If everything goes well you will find cert and key in following dirs:

Cert: /etc/letsencrypt/live/yourdomain.net/fullchain.pem Key: /etc/letsencrypt/live/yourdomain.net/privkey.pem

If you want to replace text in current directory and all it's subdirectories then use this:

find . -type f -name "*.txt" -exec sed -i 's/foo/bar/g' {} \;

If you need to find all files that was changed in system between two dates, for example 28 March 2020 and 30 March 2020 then use command below:

For example, you want to edit cron jobs, and after typing crontab -e you see that vi was opened. You can change it to nano. To do it, type:

Imagine that you have mysql dump of database (testdb.sql) and you want to restore only one table (mytable). Then do this:

sed -n -e '/DROP TABLE.*mytable/,/UNLOCK TABLES/p' testdb.sql > testdb_mytable.sql

This command will create file testdb_mytable.sql with data only for this table. Then you can import it:

To configure port mirror do this:

conf t

monitor session 1 source interface fa0/1

monitor session 1 destination interface fa0/10

Where fa0/1 is port we want to mirror and fa0/10 is destination port. This will work for Catalyst 2940, 2955, 2960, 2970, 3550, 3560, 3560-E, 3750 and 3750-E.

For Catalyst 2900XL/3500XL series use this:

conf t

int fa0/10

port monitor fa0/1

parted /dev/sdb

mkpart primary 2048s 100%

q

By default CentOS uses firewalld service to control firewall rules. If you want to configure firewall with just iptables rules, you need to do following

Disable everything of firewalld

systemctl stop firewalld.service

systemctl disable firewalld.service

Install iptables-service

yum install iptables-services

Enable and start service

systemctl enable iptables.service

systemctl start iptables.service

Now you can write rules in console and after you done type:

iptables-save

iptables -A INPUT -p tcp -s your_ip_here --dport 22 -j ACCEPT

iptables -A INPUT -p tcp -s another_your_ip_here --dport 22 -j ACCEPT

Make device offline

echo "offline" > /sys/block/sda/device/state

Delete disk

echo "1" > /sys/block/sda/device/delete

freebsd-update -r 10.3-RELEASE upgrade