[ss-manager] Fall back to /tmp if workdir is /

[xwjdsh]

I want to try using ss-manager to replace ss-server. I updated the ExecStart option, the config file located /lib/systemd/system/shadowsocks-libev.service.

...
DynamicUser=true
ExecStart=/usr/bin/ss-manager -c $CONFFILE $DAEMON_ARGS
...

Then I restarted the service, I got the following log.

Nov 23 11:59:23 eve systemd[1]: Started Shadowsocks-libev Default Server Service.
Nov 23 11:59:23 eve ss-manager[483697]:  2023-11-23 11:59:23 INFO: using tcp fast open
Nov 23 11:59:23 eve ss-manager[483697]:  2023-11-23 11:59:23 INFO: working directory points to //.shadowsocks
Nov 23 11:59:23 eve ss-manager[483697]:  2023-11-23 11:59:23 ERROR: mkdir: Read-only file system
Nov 23 11:59:23 eve ss-manager[483697]:  2023-11-23 11:59:23 ERROR: unable to create working directory
Nov 23 11:59:23 eve systemd[1]: shadowsocks-libev.service: Main process exited, code=exited, status=255/EXCEPTION
Nov 23 11:59:23 eve systemd[1]: shadowsocks-libev.service: Failed with result 'exit-code'.

I noticed that DynamicUser is used in the default systemd config, which may be why the user's workdir is '/', I thought maybe it could ignore / and use /tmp instead.