arch linux: added some troubleshooting

wiki/linux/arch-linux.md

@@ -61,3 +61,55 @@ initrd  /<installed microcode package>.img
 ```
 
 `<installed microcode package>` is either `amd-ucode` or `intel-ucode`.
+
+## Troubleshooting
+
+This section addresses problems that can occur when using Arch Linux.
+
+### Troubleshooting Setup for not Bootable Systems
+
+This section focusses on a basic guide to troubleshoot systems that are not bootable.
+To access the files of the system an Arch Linux boot stick has to be created as explained in
+[a previous section](#iso-medium).
+After booting into it set your keymap layout using the `loadkeys` setup similar to
+[the installation preparation](/wiki/linux/arch-linux/installation.md#1-preparation).
+Afterwards [mount](/wiki/linux/disk-management.md#mounting) the partition that contains the root
+file system to the `/mnt` directory.
+It is possible that LUKS encrypted file systems need to be
+[opened](/wiki/linux/dm-crypt.md#openclose-an-encrypted-volume) and then mounted using the
+`/dev/mapper` symbolic link.
+On some systems there are home or boot file system that have to be mounted on `/mnt/boot` or
+`/mnt/home` after mounting the root file system.
+Afterwards use `arch-chroot /mnt` to get into the not bootable system.
+Now the command line of the system can be accessed for troubleshooting.
+After troubleshooting `exit` the system and [unmount](/wiki/linux/disk-management.md#mounting) all previously
+mounted file systems and try to boot back into the system.
+
+Probably the most common source for not bootable systems is
+[the initial ramdisk](#problems-with-the-initial-ramdisk).
+
+### Problems with the Initial Ramdisk
+
+A common problem (especially after a interrupted update lies in the initial ramdisk environment).
+An error like this will mean that the system is
+[not bootable](#troubleshooting-setup-for-not-bootable-systems).
+To fix this generate the initial ramdisk manually as described in
+[the mkinitcpio entry](/wiki/linux/mkinitcpio.md#manually-generate-initial-ramdisk).
+
+### Stuck in Boot Screen
+
+There is a known problem described in the Arch Linux forums by
+[TheRealNubby](https://bbs.archlinux.org/viewtopic.php?id=300292) where the system goes into a
+perceived freeze after the boot process.
+This problem seems to be most prevalent on systems that use an [Nvidia](/wiki/nvidia.md) GPU
+since its only known occurences were found on Nvidia GTX 1080 GPUs.
+The boot screen will not show any errors and when
+[troubleshooting using a installation medium](#troubleshooting-setup-for-not-bootable-systems)
+logs like [the ones of SystemD](/wiki/linux/systemd.md#retrieving-the-systemd-logs) will look
+normal and won't show any errors.
+
+In this case there is the possibility that logging into Arch Linux blindly will work.
+For this type in user name and password some moments after the perceived freeze as you normally
+would do if the login screen came up.
+If the graphical interface still does not work, the command to start the graphical interface (like 
+`startx` for [X11](/wiki/linux/x_window_system.md) systems) can also work.

wiki/linux/systemd.md

@@ -43,7 +43,7 @@ Alternatively it can be enabled to start at every boot by running:
 sudo systemctl enable unturned
 ```
 
-## Start/Stop/Enable/Disable a service
+### Start/Stop/Enable/Disable a service
 
 Services can be started by running `systemctl start <service-name>`.
 They respectively can be stopped by replacing the `start`
@@ -51,3 +51,13 @@ keyword for `stop`.
 To start the service after boot it has to be enabled.
 This works accordingly with the keyword `enable`.
 The `disable` keyword stops the service from starting automatically.
+
+### Retrieving the SystemD Logs
+
+SystemD logs can easily be found using the `journalctl` command.
+One of the most notable usages of the command is for checking the logs of the previous boot.
+This can be achieved by running the following command.
+
+```sh
+journalctl -b-1
+```