AH01257: unable to connect to cgi daemon after multiple tries

[Tim Evans]

Just upgraded from F26 to F27 without incident.  However, the web 
browser interface to the "BackupPC" application 
(BackupPC-4.1.3-4.fc27.x86_64) is now broken.  The BackupPC daemon 
itself is working properly, and backups are running.

ps -ef | grep -i backup
backuppc  1130     1  0 Nov23 ?        00:00:00 /usr/bin/perl 
/usr/share/BackupPC/bin/BackupPC

However, attempting to access the browser administration pages of the 
application generates "service unavailable" (503) errors.

The Apache error log (*not* any BackupPC log) shows:

[Thu Nov 23 10:52:26.203136 2017] [cgid:error] [pid 1162:tid 
139834463086336] (13)Permission denied: [client ::1:43468] AH01257: 
unable to connect to cgi daemon after multiple tries: 
/usr/share/BackupPC/sbin/BackupPC_Admin, referer: 
http://localhost/backuppc?action=summary

Everything was working properly with F26.

Where's the permission denied coming from?

# ls -l BackupPC_Admin
-rwxr-x--- 1 backuppc apache 3924 Aug  2 12:51 BackupPC_Admin

Both apache and the BackupPC daemons are running under the userid 'backuppc'

[Patrick O'Callaghan]

On Fri, 2017-11-24 at 11:53 -0500, Tim Evans wrote:
> Everything was working properly with F26.
>
> Where's the permission denied coming from?

Is SElinux set to 'enforcing'? If so, do 'sudo setenforce 0' and try
again. If it works, the problem is with SElinux labelling. If not, it's
something else.

poc

AH01257: unable to connect to cgi daemon after multiple tries[SOLVED]

[Tim Evans]

On 11/24/2017 12:47 PM, Patrick O'Callaghan wrote:
> On Fri, 2017-11-24 at 11:53 -0500, Tim Evans wrote:
> > Everything was working properly with F26.
> >
> > Where's the permission denied coming from?
>
> Is SElinux set to 'enforcing'? If so, do 'sudo setenforce 0' and try
> again. If it works, the problem is with SElinux labelling. If not, it's
> something else.

selinux is disabled.

Turns out F27's Apache now defaults to Event MPM. Changing back to 
prefork MPM resolved this.  (Yes, I saw the performance warning in the 
Apache logs about doing this, but this instance of Apache serves only 
for BackupPC administration.)

[Richard Shaw]

I know you got your workaround in place by changing back to prefork MPM but
just an FYI, I've filed an issue upstream to see if it can be fixed
properly...

https://github.com/backuppc/backuppc/issues/170

Thanks,
Richard