feat: add check-update

Author: h3o66

commands/README.md

@@ -18,6 +18,7 @@ Replace `./gameserver` with the actual script name. Every command has a short ve
 | [Monitor](monitor.md) | `./gameserver monitor` | `./gameserver m` |
 | [Test Alert](test-alert.md) | `./gameserver test-alert` | `./gameserver ta` |
 | [Update](update.md) | `./gameserver update` | `./gameserver u` |
+| [Check Update](check-update.md) | `./gameserver check-update` | `./gameserver cu` |
 | [Force Update](force-update.md) | `./gameserver force-update` | `./gameserver fu` |
 | [Validate](validate.md) | `./gameserver validate` | `./gameserver v` |
 | [Console](console.md) | `./gameserver console` | `./gameserver c` |

commands/check-update.md

@@ -0,0 +1,44 @@
+# check-update
+
+LinuxGSM comes with an game server `check-update` command. All [SteamCMD](../steamcmd/) games servers are supported.
+
+## Commands
+
+Standard: `./gameserver check-update`
+
+Short: `./gameserver cu`
+
+Check-update will check for any available update, taking no action if no update is available. If there is an update it will send a alert if one is set up.
+
+## Automatic check for avaliupdate 
+
+### Scheduled check for updates updates
+
+A [cronjob](../configuration/cronjobs.md) can be set to run `check-update` at any given time.
+
+Currently a cronjob is only makes sense if a [Alert](../alerts/README.md) is set up.
+
+To edit cronjobs, type:
+
+`crontab -e`
+
+A cronjob can be run as the `gameserver user` or as `root`, this choice is down to personal preference. Remember to amend the examples to match a specific game server.
+
+Here is an example of a user based cronjob to check for an update once an hour.
+
+```text
+0 * * * * /home/username/gameserver check-update > /dev/null 2>&1
+```
+
+Here is an example of a root based cronjob to check for an check-update once an hour.
+
+{% hint style="info" %}
+The extra `su - username -c` indicates which user to run the script as.
+{% endhint %}
+
+```text
+0 * * * * su - username -c '/home/username/gameserver update' > /dev/null 2>&1
+```
+
+[crontab.guru](https://crontab.guru/) is a great resource to generate cronjobs.
+