Documents good sysadmin solutions and oneliners to problems.

sysadmin.md

Scp files between two servers without the need to first copy the file locally.

scp -3 'username@server1:/home/user/filename.tar.gz' username@server2:/home/user/

Create point to point tunnel between two servers over ssh with a tun interface to avoid the need to open a firewall.

cli># ssh -w5:5 root@hserver
srv># ifconfig tun5 10.0.1.1 netmask 255.255.255.252   
cli># ifconfig tun5 10.0.1.2 netmask 255.255.255.252   

Oneliner to list block percentage on a filesystem

dumpe2fs -h /dev/sda1 2> /dev/null | awk -F ':' '{ if($1 == "Reserved block count") { rescnt=$2 } } { if($1 == "Block count") { blkcnt=$2 } } END { print "Reserved blocks: "(rescnt/blkcnt)*100"%" }'

Set block percentage

tune2fs -m1 /dev/sda1

Write line number and function name when debug bash script.

export PS4='+(${BASH_SOURCE}:${LINENO}): ${FUNCNAME[0]:+${FUNCNAME[0]}(): }'
$ bash -x ./script

Run command as a service

$ socat TCP-LISTEN:6666,fork,reuseaddr exec:/command

Forward port to a different port.

socat TCP-LISTEN:9999,reuseaddr,fork,su=nobody TCP:nighter.se:80

socat TCP-LISTEN:80,fork TCP:<address>:80

TLS termination and MITM proxy

 openssl req -new -x509 -keyout test.key -out test.crt -node
 cat test.key test.crt > cert.pem
 socat -v openssl-listen:443,reuseaddr,cert=./cert.pem,verify=0,fork tcp4:xx.xx.xx.xx:80

Log everything from terminal to file

exec >> /var/log/logfile 2>&1

Clone driver over ssh and create virtualbox image.

 ssh root@host "dd if=/dev/sda | gzip -1 -" | dd of=image.gz status=progress    
 gunzip image.gz
 VBoxManage convertfromraw image.bin image.vdi --format VDI

Fix gpg when switch yubikey

gpgconf --kill gpg-agent
gpg --card-status

Jq magic

{
"Items": {
   "password": {
       "S": "password"   
   },
   "username": {
   "S": "username"
   }   
}

Example JQ parsing

 <command_output_json> | jq -r '.Items[] | "\(.username[]):\(.password[])"'

sshfs

sudo sshfs -o allow_other,default_permissions username@server:/home/username/debug /mnt/debug

Relink libc on binary

patchelf --set-interpreter ${pkgs.glibc}/lib/ld-linux-x86-64.so.2 ~/bin/hetty

Setup sound

pavucontrol