Add and use default_backend to set individual backend defaults to auto

config/paths-common.conf

@@ -7,11 +7,13 @@ after  = paths-overrides.local
 
 [DEFAULT]
 
+default_backend = auto
+
 sshd_log = %(syslog_authpriv)s
-sshd_backend = auto
+sshd_backend = %(default_backend)s
 
 dropbear_log = %(syslog_authpriv)s
-dropbear_backend = auto
+dropbear_backend = %(default_backend)s
 
 # There is no sensible generic defaults for syslog log targets, thus
 # leaving them empty here so that no errors while parsing/interpolating configs
@@ -20,8 +22,8 @@ syslog_ftp =
 syslog_local0 =
 syslog_mail_warn =
 syslog_user =
-# Set the default syslog backend target to auto
-syslog_backend = auto
+# Set the default syslog backend target to default_backend
+syslog_backend = %(default_backend)s
 
 # from /etc/audit/auditd.conf
 auditd_log = /var/log/audit/audit.log
@@ -42,17 +44,17 @@ suhosin_log = %(syslog_user)s %(lighttpd_error_log)s
 
 # defaults to ftp or local2 if ftp doesn't exist
 proftpd_log = %(syslog_ftp)s
-proftpd_backend = auto
+proftpd_backend = %(default_backend)s
 
 # http://svnweb.freebsd.org/ports/head/ftp/proftpd/files/patch-src_proftpd.8.in?view=markup
 # defaults to ftp but can be overwritten.
 pureftpd_log = %(syslog_ftp)s
-pureftpd_backend = auto
+pureftpd_backend = %(default_backend)s
 
 # ftp, daemon and then local7 are tried at configure time however it is overwriteable at configure time
 #
 wuftpd_log = %(syslog_ftp)s
-wuftpd_backend = auto
+wuftpd_backend = %(default_backend)s
 
 # syslog_enable defaults to no. so it defaults to vsftpd_log_file setting of /var/log/vsftpd.log
 # No distro seems to set it to syslog by default
@@ -61,16 +63,16 @@ vsftpd_log = /var/log/vsftpd.log
 
 # Technically syslog_facility in main.cf can overwrite but no-one sane does this.
 postfix_log = %(syslog_mail_warn)s
-postfix_backend = auto
+postfix_backend = %(default_backend)s
 
 dovecot_log = %(syslog_mail_warn)s
-dovecot_backend = auto
+dovecot_backend = %(default_backend)s
 
 # Seems to be set at compile time only to LOG_LOCAL0 (src/const.h) at Notice level
 solidpop3d_log = %(syslog_local0)s
 
 mysql_log = %(syslog_daemon)s
-mysql_backend = auto
+mysql_backend = %(default_backend)s
 
 roundcube_errors_log = /var/log/roundcube/errors