我正在尝试在我的 ubuntu 服务器 16.04 上安装 fail2ban 服务，但是我有这个错误并且 fail2ban 服务无法启动，这是什么问题？
root@clm:~# apt install fail2ban
Reading package lists... Done
Building dependency tree
Reading state information... Done
fail2ban is already the newest version (0.9.3-1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Setting up fail2ban (0.9.3-1) ...
Job for fail2ban.service failed because the control process exited with error code. See "systemctl status fail2ban.service" and "journalctl -xe" for details.
invoke-rc.d: initscript fail2ban, action "start" failed.
● fail2ban.service - Fail2Ban Service
Loaded: loaded (/lib/systemd/system/fail2ban.service; enabled; vendor preset: enabled)
Active: activating (auto-restart) (Result: exit-code) since Fri 2017-12-29 18:08:01 CET; 8ms ago
Docs: man:fail2ban(1)
Process: 4888 ExecStart=/usr/bin/fail2ban-client -x start (code=exited, status=255)
Dec 29 18:08:01 domain systemd[1]: Failed to start Fail2Ban Service.
Dec 29 18:08:01 domain systemd[1]: fail2ban.service: Unit entered failed state.
Dec 29 18:08:01 domain systemd[1]: fail2ban.service: Failed with result 'exit-code'.
dpkg: error processing package fail2ban (--configure):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
fail2ban
E: Sub-process /usr/bin/dpkg returned an error code (1)
日志说是这样的，
root@clm:~# systemctl status fail2ban.service
● fail2ban.service - Fail2Ban Service
Loaded: loaded (/lib/systemd/system/fail2ban.service; enabled; vendor preset: enabled)
Active: inactive (dead) (Result: exit-code) since Fri 2017-12-29 18:27:09 CET; 9min ago
Docs: man:fail2ban(1)
Process: 7277 ExecStop=/usr/bin/fail2ban-client stop (code=exited, status=0/SUCCESS)
Process: 7301 ExecStart=/usr/bin/fail2ban-client -x start (code=exited, status=255)
Main PID: 7026 (code=killed, signal=TERM)
Dec 29 18:27:09 domain systemd[1]: fail2ban.service: Control process exited, code=exited status=255
Dec 29 18:27:09 domain systemd[1]: Failed to start Fail2Ban Service.
Dec 29 18:27:09 domain systemd[1]: fail2ban.service: Unit entered failed state.
Dec 29 18:27:09 domain systemd[1]: fail2ban.service: Failed with result 'exit-code'.
Dec 29 18:27:09 domain systemd[1]: fail2ban.service: Service hold-off time over, scheduling restart.
Dec 29 18:27:09 domain systemd[1]: Stopped Fail2Ban Service.
Dec 29 18:27:09 domain systemd[1]: fail2ban.service: Start request repeated too quickly.
Dec 29 18:27:09 domain systemd[1]: Failed to start Fail2Ban Service.
root@clm:~# tail -f /var/log/fail2ban.log
2017-12-29 18:26:08,198 fail2ban.actions [7026]: INFO Set banTime = 600
2017-12-29 18:26:08,262 fail2ban.filter [7026]: INFO Added logfile = /var/log/auth.log
2017-12-29 18:26:08,330 fail2ban.filter [7026]: INFO Set jail log file encoding to UTF-8
2017-12-29 18:26:08,331 fail2ban.filter [7026]: INFO Set maxRetry = 5
2017-12-29 18:26:08,331 fail2ban.filter [7026]: INFO Set maxlines = 10
2017-12-29 18:26:08,448 fail2ban.server [7026]: INFO Jail sshd is not a JournalFilter instance
2017-12-29 18:26:08,465 fail2ban.jail [7026]: INFO Jail 'sshd' started
2017-12-29 18:27:05,924 fail2ban.server [7026]: INFO Stopping all jails
2017-12-29 18:27:06,756 fail2ban.jail [7026]: INFO Jail 'sshd' stopped
2017-12-29 18:27:06,831 fail2ban.server [7026]: INFO Exiting Fail2ban