How to check whether a full reboot is required

Determine whether a full CentOS 7 reboot is required and which services need to be restarted.

Operating system.

$ cat /etc/centos-release
CentOS Linux release 7.6.1810 (Core)

I will use needs-restarting utility that reports running processes that have been updated.

This utility is provided by the yum-utils package.

$ yum --cacheonly whatprovides needs-restarting 
Loaded plugins: fastestmirror
yum-utils-1.1.31-52.el7.noarch : Utilities based around the yum package manager
Repo        : base
Matched from:
Filename    : /usr/bin/needs-restarting

Use it determine whether a full reboot is required.

It will return 1 when reboot is required and give you additional feedback.
$ sudo needs-restarting --reboothint
Core libraries or services have been updated:
  glibc -> 2.17-292.el7

Reboot is required to ensure that your system benefits from these updates.

More information:
https://access.redhat.com/solutions/27943
$ echo $?
1
$ sudo needs-restarting --reboothint
Core libraries or services have been updated:
  systemd -> 219-67.el7_7.2
  kernel -> 3.10.0-1062.9.1.el7
  dbus -> 1:1.10.24-13.el7_6
  openssl-libs -> 1:1.0.2k-19.el7
  linux-firmware -> 20190429-72.gitddde598.el7
  glibc -> 2.17-292.el7

Reboot is required to ensure that your system benefits from these updates.

More information:
https://access.redhat.com/solutions/27943
$ echo $?
1
It will return 0 when reboot is not required.
$ sudo needs-restarting --reboothint
No core libraries or services have been updated.
Reboot is probably not necessary.
$ echo $?
0

Use it also determine services that are affected by updates.

$ sudo needs-restarting --services
rpcbind.service
chronyd.service
sshd.service
systemd-logind.service
NetworkManager.service
postfix.service
tuned.service
auditd.service
[email protected]
crond.service
rsyslog.service
dbus.service
gssproxy.service
systemd-udevd.service
systemd-journald.service
polkit.service

Notice, it will always return 0, so do not use exit code in this specific case.