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Unix tips & troubleshooting

GCP - SELinux commands for GitHub Actions runner in CentOS

sudo semanage fcontext --add --type initrc_exec_t /<fullpath>/runsvc.sh
restorecon -v /<fullpath>/runsvc.sh
sudo ./svc.sh start
sudo ./svc.sh status

Generate ed25519 keypair & add to remote SSH

Generate ed25519 keypair:
ssh-keygen -t ed25519 -C "[email protected]"

The public and private key pair will be saved, for example, in ~/.ssh/id_x and ~/.ssh/id_x.pub. The .pub file is the public key.

Configure remote SSH system to accept passwordless login:

  • open ~/.ssh/authorized_hosts in your preferred editor
  • copy the PUBLIC key to a new line
    ssh-ed25519 publicKey [email protected]

SSH - Backspace doesn't work

add to ~/.ssh/config

Host *
    SetEnv TERM=xterm-256color

Wiping a drive

dd if=/dev/zero of=/dev/sda bs=512
or
dd if=/dev/random of=/dev/sda bs=512
Can be used to wipe a drive and overwritten with zeroes or randoms. This can be done in a liveboot of gparted to see if the correct drive is selected.

iptables - Open webserver ports (HTTP and HTTPS)

HTTP (80)

sudo iptables -I INPUT -p tcp --dport 80 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT

sudo iptables -I OUTPUT -p tcp --sport 80 -m conntrack --ctstate ESTABLISHED -j ACCEPT

HTTPS (443)

sudo iptables -I INPUT -p tcp --dport 443 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT

sudo iptables -I OUTPUT -p tcp --sport 443 -m conntrack --ctstate ESTABLISHED -j ACCEPT