Description of problem:
Services that supply User= directives but not Group= directives in their service files end up with processes that have GIDs equal to their UIDs instead of the given users' primary GIDs as systemd.exec(5) suggests.  For example, if a service file refers to a user with UID 1 and GID 2 and it does not explicitly specify a group, the resulting process will have GID 1.


Version-Release number of selected component (if applicable):
systemd-26-8.fc15.x86_64


How reproducible:
Always


Steps to Reproduce:
1. groupadd -g 255 testgroup
2. useradd -g 255 -u 256 testuser
3. echo -e '#!/bin/sh\nlogger `id`' > /usr/bin/log_id.sh
4. cat > /etc/systemd/system/bugtest.service << EOF
[Unit]
Description=Bug test

[Service]
Type=oneshot
User=testuser
ExecStart=/usr/bin/log_id.sh
EOF
5. systemctl start bugtest.service
6. grep testuser /var/log/messages


Actual results:
logger: uid=256(testuser) gid=256 groups=255(testgroup),256


Expected results:
logger: uid=256(testuser) gid=255(testgroup) groups=255(testgroup)