Incomplete output of upgrade.log while performing an in-place upgrade from Red Hat Enterprise Linux 6 to Red Hat Enterprise Linux 7

Issue

While running redhat-upgrade-tool on bare metal machines to perform an in-place upgrade from RHEL6 to RHEL7, the upgrade output logged to /var/log/upgrade.log is incomplete.
During the upgrade observe the output seen on the system console:

[ 1121.460471] upgrade-post[10951]: Running /root/preupgrade/postupgrade.d/z_copy_clean_conf.sh...
[ 1121.567347] upgrade-post[10951]: Config file /etc/sysconfig/sendmail already exists. Move to /etc/sysconfig/sendmail.preupg
[ 1121.703339] upgrade-post[10951]: Copy file etc/sysconfig/sendmail to /etc/sysconfig/sendmail
[ 1121.806448] upgrade-post[10951]: Config file /etc/yum.conf already exists. Move to /etc/yum.conf.preupg
[ 1121.921397] upgrade-post[10951]: Copy file etc/yum.conf to /etc/yum.conf
[ 1122.003355] upgrade-post[10951]: Config file /etc/rpc already exists. Move to /etc/rpc.preupg
[ 1122.106387] upgrade-post[10951]: Copy file etc/rpc to /etc/rpc
[ 1122.178414] upgrade-post[10951]: Config file /etc/prelink.conf already exists. Move to /etc/prelink.conf.preupg
[ 1122.300383] upgrade-post[10951]: Copy file etc/prelink.conf to /etc/prelink.conf
[ 1122.391404] upgrade-post[10951]: Config file /etc/inputrc already exists. Move to /etc/inputrc.preupg
[ 1122.504389] upgrade-post[10951]: Copy file etc/inputrc to /etc/inputrc
[ 1122.584388] upgrade-post[10951]: Config file /etc/hosts already exists. Move to /etc/hosts.preupg
[ 1122.693375] upgrade-post[10951]: Copy file etc/hosts to /etc/hosts
[ 1122.769375] upgrade-post[10951]: Config file /etc/exports already exists. Move to /etc/exports.preupg
[ 1122.882383] upgrade-post[10951]: Copy file etc/exports to /etc/exports
[ 1122.962389] upgrade-post[10951]: Config file /etc/shells already exists. Move to /etc/shells.preupg
[ 1123.073375] upgrade-post[10951]: Copy file etc/shells to /etc/shells
[ 1123.151366] upgrade-post[10951]: Config file /etc/pki/nssdb/key3.db already exists. Move to /etc/pki/nssdb/key3.db.preupg
[ 1123.285385] upgrade-post[10951]: Copy file etc/pki/nssdb/key3.db to /etc/pki/nssdb/key3.db
[ 1123.386389] upgrade-post[10951]: Config file /etc/pki/nssdb/secmod.db already exists. Move to /etc/pki/nssdb/secmod.db.preupg
[ 1123.523457] upgrade-post[10951]: Copy file etc/pki/nssdb/secmod.db to /etc/pki/nssdb/secmod.db
[ 1123.628401] upgrade-post[10951]: Config file /etc/pki/nssdb/cert8.db already exists. Move to /etc/pki/nssdb/cert8.db.preupg
         Stopping Device-Mapper Multipath Device Controller...
[ 1123.764232] upgrade-post[10951]: Copy file etc/pki/nssdb/cert8.db to /etc/pki/nssdb/cert8.db
         Stopping Debug shell on tty2...
[ 1123.934260] upgrade-post[10951]: Config file /etc/pki/nssdb/key4.db already exists. Move to /etc/pki/nssdb/key4.db.preupg
[  OK  ] Stopped Debug shell on tty2.
[ 1124.112228] upgrade-post[10951]: Copy file etc/pki/nssdb/key4.db to /etc/pki/nssdb/key4.db
[  OK  [ 1124.263195] ] upgrade-postStopped Device-Mapper Multipath Device Controller.[10951]:
Config file /etc/pki/nssdb/cert9.db already exists. Move to /etc/pki/nssdb/cert9.db.preupg
[  OK  ] Stopped System Upgrade (post).
[ 1124.472251] upgrade-post[10951]: Copy file etc/pki/nssdb/cert9.db to /etc/pki/nssdb/cert9.db
[ 1124.628158] upgrade-post[10951]: Config file /etc/pki/nssdb/pkcs11.txt already exists. Move to /etc/pki/nssdb/pkcs11.txt.preupg[
  OK  ] Stopped target System Upgrade.
[ 1124.628310] [upgrade-post  OK  [10951]: ] Copy file etc/pki/nssdb/pkcs11.txt to /etc/pki/nssdb/pkcs11.txtStopped target Sockets.

[  OK  ] [ 1124.970199] Closed Open-iSCSI iscsiuio Socket.upgrade-post
[10951]: Config file /etc/default/nss already exists. Move to /etc/default/nss.preupg
[[ 1125.146208] [ 1134.674451] systemd[1]: Stopping Journal Service...
  OK  upgrade-post] [10951]: Stopped target System Initialization.Copy file etc/default/nss to /etc/default/nss

         Stopping Journal Service...
[ 1125.353221] upgrade-post[10951]: Config file /etc/pam.d/system-auth already exists. Move to /etc/pam.d/system-auth.preupg
[  OK  ] Stopped Apply Kernel Variables.
[ 1135.109958] systemd[1]: Stopped Apply Kernel Variables.
[ 1135.172865] systemd[1]: Stopping Apply Kernel Variables...
         Stopping Apply Kernel Variables...[ 1125.527760]
upgrade-post[10951]: Copy file etc/pam.d/system-auth to /etc/pam.d/system-auth
[  OK  ] Stopped target Local Encrypted Volumes.
[ 1135.447978] systemd[1]: Stopped target Local Encrypted Volumes.
[ 1135.519144] systemd[1]: Stopping Local Encrypted Volumes.
[ 1125.711200] [upgrade-post  OK  [10951]: ] Config file /etc/pam.d/system-auth.PreKRB5clnt already exists. Move to /etc/pam.d/system-auth.PreKRB5clnt.preupgStopped Setup Virtual Console.

[ 1135.794975] systemd[1]: Stopped Setup Virtual Console.
[ 1135.856797] systemd[1]: Stopping Setup Virtual Console...
[ 1126.056404]  [ 1135.922008] systemd[1]: Stopping udev Kernel Device Manager...
        upgrade-postStopping Setup Virtual Console...[10951]:
Copy file etc/pam.d/system-auth.PreKRB5clnt to /etc/pam.d/system-auth.PreKRB5clnt
[ 1126.636187] upgrade-post[10951]: Config file /etc/postfix/main.cf already exists. Move to /etc/postfix/main.cf.preupg
Stopping udev Kernel Device Manager...
[ 1126.636348] upgrade-post[10951]: Copy file etc/postfix/main.cf to /etc/postfix/main.cf
[ 1126.912166] upgrade-post[10951]: [Config file /usr/share/info/dir already exists. Move to /usr/share/info/dir.preupg  OK
] Stopped udev Coldplug all Devices.
[ 1136.624009] systemd[1]: Stopped udev Coldplug all Devices.
[1136.689996] systemd[1]: Stopping udev Coldplug all Devices...
[ 1126.912336]          upgrade-postStopping udev Coldplug all Devices...[10951]:
Copy file usr/share/info/dir to /usr/share/info/dir
[ 1127.375169] upgrade-post[10951]: [Config file /var/lib/logrotate.status does not exists.  OK
] Stopped target Local File Systems.
[ 1137.056011] systemd[1]: Stopped target Local File Systems.
[ 1137.121976] systemd[1]: Stopping Local File Systems.
[ 1137.122311] systemd[1]: Unmounting /mnt/sys/fs/cgroup/hugetlb...
[ 1127.375331]  [ 1137.254092] systemd[1]: Unmounting /sysroot/sys/fs/cgroup/devices...
        upgrade-postUnmounting /mnt/sys/fs/cgroup/hugetlb...[10951]:
Copy file var/lib/logrotate.status to /var/lib/logrotate.status
[ 1127.963164] upgrade-post[10951]: Config file /var/lib/prelink/quick already exists. Move to /var/lib/prelink/quick.preupg
         Unmounting /sysroot/sys/fs/cgroup/devices...
[ 1127.963307] u[ 1137.682345] systemd[1]: Unmounting /sysroot/sys/kernel/security...
pgrade-post[10951]: Copy file var/lib/prelink/quick to /var/lib/prelink/quick
[ 1128.329168] upgrade-post[10951]: Config file /var/lib/prelink/full already exists. Move to /var/lib/prelink/full.preupg
         Unmounting /sysroot/sys/kernel/security...
[ 1128.329312] u[ 1138.044367] systemd[1]: Unmounting /sysroot/sys/fs/cgroup/cpuset...
pgrade-post[10951]: Copy file var/lib/prelink/full to /var/lib/prelink/full
[ 1128.690163] upgrade-post[10951]: Config file /var/log/mail/statistics already exists. Move to /var/log/mail/statistics.preupg
         Unmounting /sysroot/sys/fs/cgroup/cpuset...
[ 1128.690301] u[ 1138.411424] systemd[1]: Unmounting /sysroot/sys/fs/cgroup/net_cls,net_prio...
pgrade-post[10951]: Copy file var/log/mail/statistics to /var/log/mail/statistics
[ 1129.074186] upgrade-post[10951]: Config file /var/log/prelink/prelink.log already exists. Move to /var/log/prelink/prelink.log.preupg
         Unmounting /sysroot/sys/fs/cgroup/net_cls,net_prio...
[ 1129.074337] u[ 1138.815371] systemd[1]: Unmounting /mnt/sys/fs/cgroup/cpuset...
pgrade-post[10951]: Copy file var/log/prelink/prelink.log to /var/log/prelink/prelink.log
[ 1129.471167] upgrade-post[10951]: Config file /var/run/nscd/nscd.pid does not exists.
         Unmounting /mnt/sys/fs/cgroup/cpuset...
[ 1129.471295] u[ 1139.146373] systemd[1]: Unmounting /mnt/sys/fs/cgroup/freezer...
pgrade-post[10951]: Copy file var/run/nscd/nscd.pid to /var/run/nscd/nscd.pid
         Unmounting /mnt/sys/fs/cgroup/freezer...
[ 1129.792143] u[ 1139.374406] systemd[1]: Unmounting /mnt/sys/fs/cgroup/net_cls,net_prio...
pgrade-post[10951]: redhat_upgrade_tool.util WARNING: failed to remove /system-upgrade-root: [Errno 16] Device or resource busy: '/system-upgrade-root/mnt'
[ 1130.110165] upgrade-post[10951]:          resetting bootloader configUnmounting /mnt/sys/fs/cgroup/net_cls,net_prio...

[ 1130.110322] u[ 1139.770396] systemd[1]: Unmounting /sysroot/sys/fs/cgroup/cpu,cpuacct...
pgrade-post[10951]: removing boot images
[ 1130.384184] upgrade-post[10951]: removing downloaded packages
         Unmounting /sysroot/sys/fs/cgroup/cpu,cpuacct...
[ 1130.384329] u[ 1140.044408] systemd[1]: Unmounting /sysroot/sys/fs/cgroup/perf_event...
pgrade-post[10951]: removing miscellaneous files
         Unmounting /sysroot/sys/fs/cgroup/perf_event...
[ 1130.665788] u[ 1140.254428] systemd[1]: Unmounting /mnt/sys/fs/cgroup/systemd...
pgrade-post[10951]: all upgrade scripts finished
[ 1130.868168] u[ 1140.400888] systemd-journald[4381]: Received SIGTERM from PID 1 (systemd).
pgrade-post[10951]: writing logs to disk and rebooting
...

The contents of /var/log/upgrade.log shown below contain significantly less information than the system console output above:

May 02 15:10:58 oo-node13 upgrade-post[10951]: Config file /etc/hosts already exists. Move to /etc/hosts.preupg
May 02 15:10:58 oo-node13 upgrade-post[10951]: Copy file etc/hosts to /etc/hosts
May 02 15:10:58 oo-node13 upgrade-post[10951]: Config file /etc/exports already exists. Move to /etc/exports.preupg
May 02 15:10:58 oo-node13 upgrade-post[10951]: Copy file etc/exports to /etc/exports
May 02 15:10:58 oo-node13 upgrade-post[10951]: Config file /etc/shells already exists. Move to /etc/shells.preupg
May 02 15:10:58 oo-node13 upgrade-post[10951]: Copy file etc/shells to /etc/shells
May 02 15:10:58 oo-node13 upgrade-post[10951]: Config file /etc/pki/nssdb/key3.db already exists. Move to /etc/pki/nssdb/key3.db.preupg
May 02 15:10:58 oo-node13 upgrade-post[10951]: Copy file etc/pki/nssdb/key3.db to /etc/pki/nssdb/key3.db
May 02 15:10:58 oo-node13 upgrade-post[10951]: Config file /etc/pki/nssdb/secmod.db already exists. Move to /etc/pki/nssdb/secmod.db.preupg
May 02 15:10:58 oo-node13 upgrade-post[10951]: Copy file etc/pki/nssdb/secmod.db to /etc/pki/nssdb/secmod.db