If I run something like this:
ssh -4 -f -N -T -R "/home/dude/lol.socket:192.168.4.44:4444" dude@someserver -p 22 -i privatekey -o "ExitOnForwardFailure yes" -o ConnectTimeout=5 -o ConnectionAttempts=3 -o ServerAliveInterval=15 -o
And then lets say the connection is closed or dies for whatever reason.. say the computer reboots due to maintenance or error or there's internet connectivity issues or whatever -> we have a big problem. The created socket file /home/dude/lol.socket
on the someserver
does not get deleted by sshd. So as the reverse tunnel initiator is recovering and tries to recreate the tunnel it can't because:
Error: remote port forwarding failed for listen path /home/dude/lol.socket
On the server side you get something like:
error: bind: Address already in use
error: unix_listener: cannot bind to path: /home/dude/lol.socket
What would be the supported way / best hack to cleanup the socket after disconnect? Is this a bug in sshd, shouldn't it do that automatically if/when disconnects are noticed?
Backstory:
The idea behind using the sockets is simply that the server is going to handle n "dudes" creating reverse tunnels for m "lol" services in whatever ports and using sockets makes it much easier to ensure that a "dude" can only access and bind to his own sockets, but not other dudes sockets. It also frees me from having to keep record of which dude is using which port to expose which service. And when dude wants to connect to the service on some other server all he needs to know is the name of the service and bind it to some random local port (or socket if he wants to) i.e.
ssh -v -i -4 -N -T -L "127.0.0.1:3334:/home/dude/lol.sock" -p 22 dude@someserver -o "ExitOnForwardFailure yes" -o ConnectTimeout=5 -o ConnectionAttempts=3 -o ServerAliveInterval=15 -o ServerAliveCountMax=3
There's no need to know some magic port number that the reverse tunnel on the server is suppose to be running on. So, if you have better ideas how to solve this issue I'm all ears.
Tested with client/server both running Debian 9
(client actually on mac inside docker container) using openssh-client/server version 7.4p1-10+deb9u2
autossh
autossh
solve my problem with the sockets on the server not being cleared? I thought it's basically a client side wrapper around ssh to detect broken tunnels and recreate them?/run/user/1000/
and so on you could use instead. This is a tmpfs lost on reboot.netstat -a --unix
and cross reference that to all socket files I can find based on our naming convention and delete all socket files that weren't listed by netstat. This is now run on cron every minute. It seems to be working alright, maybe I'll post it as an answer at some point if better candidates do not appear. Probly should move the files under/run
anyway though as putting them under home directories is rather unorthodox. So thanks @meuh for reminding about that. :)