The @ symbol and systemctl and vsftpd
I have a two part question.
What is the significance of the @ symbol in systemctl scripts?
How to start vsftpd in fedora 16, (which in some tutorials seems to contain an @ in it's name)? I have done everything the tutorials say, and it still gives me an error. http://blog.tuxforge.com/fedora-16-vsftpd/
What I've done
systemctl enable [email protected]
What I see
Failed to issue method call: No such file or directory
(I have tried this with a absolute path as well, and after I checked there is no such file. The real file does not contain an @ sign, and is located under the /lib/systemd/system/ directory. I have also tried starting and enabling with and without the @ symbol, enabling works, but starting doesn't. I realize the article is now obsolete, but I still cannot seem to start the service. When I try to connect it doesn't let me)
EDIT: I got the service to start somehow, but I would still like to know what the @ symbol means in some service names. Also I am still getting a login error number #500 cannot change directory [...], what does this mean?
To start it I just typed
sudo systemctl enable vsftpd.service
sudo systemctl start vsftpd.service (the problem was I was using an absolute path for this I think)
Solution 1:
The @ symbol is for special services, sockets, and other units where multiple instances can be run.
For instance, [email protected] is the service that provides text login terminals. When you press Ctrl+Alt+F2, [email protected] is started, creating virtual terminal #2.
Another service that uses this functionality is OpenVPN. You can create a file /etc/openvpn/work.conf, configured to connect to the VPN at your workplace, and then systemctl start [email protected] to connect to it. Similarly, you could create /etc/openvpn/home.conf, then start [email protected] if you had a VPN at home. This prevents you from having to create a .service file for every VPN you connect to.
But don't take my word for it. Try it out! Let's create a simple service that outputs a message to syslog. Create a file /etc/systemd/system/[email protected] with the following contents:
[Unit]
Description=Echo '%I'
[Service]
Type=oneshot
ExecStart=/bin/echo %i
StandardOutput=syslog
Notice the %i? systemd will populate that with whatever follows the @ sign when the service is started. So, try starting [email protected]:
systemctl start [email protected]
Then, check the journal:
journalctl -n10
At the bottom, you'll see that systemd ran /bin/echo foo:
Feb 24 12:41:01 localhost echo[8412]: foo
Now, try systemctl start [email protected]. This time, systemd will populate %i with bar, so you'll see:
Feb 24 12:42:51 localhost echo[8432]: bar
That's all there is to it! Anything could potentially follow the @ sign, as systemd just replaces %i in the service definition with it. OpenVPN uses it for configuration, other services might use for something else, like a port number.
For more information, see man systemd.unit.