Comment 7 for bug 1256695

I'm running into this as well.

On:
---
Description: Ubuntu 14.04 LTS
Release: 14.04
Codename: trusty

Running:
-------
rsyslog 7.4.4-1ubuntu2

/var/log permissions are:
---------------------------
drwxrwxr-x 6 root root 4096 Apr 30 07:11 log

Running rsyslog in the foreground with debugging flags results in this sequence of messages:

2009.061284547:7f7636f81780: cnf:global:cfsysline: $PrivDropToUser syslog
2009.061356413:7f7636f81780: uid 101 obtained for user 'syslog'
2009.061373099:7f7636f81780: cnf:global:cfsysline: $PrivDropToGroup syslog
2009.061464895:7f7636f81780: gid 103 obtained for group 'syslog'
...
2009.173401545:7f763387f700: file '/var/log/syslog' opened as #-1 with mode 416
2009.173429557:7f763387f700: strm 0x7f762c000b70: open error 13, file '/var/log/syslog': Permission denied

As mentioned in other comments, possible workarounds are:
0. Touch (and ensure syslog:adm perm) on the file before the daemon starts
1. Make /var/log permissions more permissive (allowing adm to write to it).