2018/11/18 UUCP at userland

UUCP is an (old) way of synchronizing files between systems. But there are still some reasons why someone (at least I) wants to use it still today. It can be invoked at any time weather the remote system is reachable or not, can continue interrupted transfers very well and supports transparent switching to different transport layers.

In my case I don’t own the server that is my standard remote for all these things, so I needed to figure out an way how to install uucp as a user. It isn’t hard and there is only one place where you have to pay attention. The way described here works for on an uberspace server (Uberspace). When uucp is installed in this way, the binaries are not setuid/setgid, but that is also not necessary because everything is already running with my uid/gid so no permission escalation is necessary.

Installing UUCP

Installing uucp is very simple on uberspace, you just call toast arm uucp. Toast is a program that is already installed on uberspace and automatically downloads, compiles and installs programs to the home dir of an user. (For more details look at the uberspace wiki) Toast automatically configures the program with the prefix set to ~/.toast/armed, so the uucp config file is found at ~/.toast/armed/conf/uucp/config

Configuring UUCP

The config file (mainly) setups all paths of uucp and the uucp name of the host

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uuname volans

spool /home/salias/uucp/spool
pubdir /home/salias/uucp/pub
lockdir /home/salias/uucp/lock

max-uuxqts 1

sysfile /home/salias/uucp/sys
portfile /home/salias/uucp/port
#dialfile
#dailcodefile
callfile /home/salias/uucp/call
passwdfile /home/salias/uucp/passwd
logfile /home/salias/uucp/log
statfile /home/salias/uucp/stat
debugfile /home/salias/uucp/debug

With this config file, all other config files for uucp are in the uucp folder in my home dir. In this folder there are some more direcories: bin, lock, spool and pub. Pub is a bit special, uucp requires that this folder is world accessible, but only this folder. So my current permissions for this folder are drwxrwx-wt, but my home dir is only accessible to me, that makes it save again.

Configuring remote access to uucp

In my case, the transport layer used is uucp over ssh, so there is the need to provide access to uucp via ssh. This is done via a special ssh-key for each client. The relevant part of ~/.ssh/authorized_keys is

no-port-forwarding,no-X11-forwarding,no-agent-forwarding,command="/home/salias/.toast/armed/bin/uucico -l"

in front of the public key.