42 Common problems and their solutions #

If you encounter any problems using the SUSE Linux Enterprise Server installation media, check the integrity of your installation media. Boot from the media and choose Check Installation Media from the boot menu. In a running system, start YaST and choose Software › Media Check. To check the SUSE Linux Enterprise Server medium, insert it into the drive and click Start Check in the Media Check screen of YaST. This may take several minutes. If errors are detected, do not use this medium for installation. Media problems may occur when having burned the medium yourself. Burning the media at a low speed (4x) helps to avoid problems.

Figure 42.1: Checking Media #

 

If your computer does not contain a bootable DVD-ROM drive or if the one you have is not supported by Linux, there are several options you can install your machine without a built-in DVD drive:

One reason a machine does not boot the installation media can be an incorrect boot sequence setting in BIOS. The BIOS boot sequence must have DVD drive set as the first entry for booting. Otherwise the machine would try to boot from another medium, typically the hard disk. Guidance for changing the BIOS boot sequence can be found the documentation provided with your mainboard, or in the following paragraphs.

The BIOS is the software that enables the very basic functions of a computer. Motherboard vendors provide a BIOS specifically made for their hardware. Normally, the BIOS setup can only be accessed at a specific time—when the machine is booting. During this initialization phase, the machine performs several diagnostic hardware tests. One of them is a memory check, indicated by a memory counter. When the counter appears, look for a line, usually below the counter or somewhere at the bottom, mentioning the key to press to access the BIOS setup. Usually the key to press is one of Del, F1, or Esc. Press this key until the BIOS setup screen appears.

Regardless of what language and keyboard layout your final installation will be using, most BIOS configurations use the US keyboard layout as shown in the following figure:

Figure 42.2: US Keyboard Layout #

 

Some hardware types, mainly very old or very recent ones, fail to install. Often this may happen because support for this type of hardware is missing in the installation kernel, or because of certain functionality included in this kernel, such as ACPI, that can still cause problems on some hardware.

If your system fails to install using the standard Installation mode from the first installation boot screen, try the following:

If this fails, proceed as above, but choose Safe Settings instead. This option disables ACPI and DMA support. Most hardware will boot with this option.

If both of these options fail, use the boot options prompt to pass any additional parameters needed to support this type of hardware to the installation kernel. For more information about the parameters available as boot options, refer to the kernel documentation located in /usr/src/linux/Documentation/kernel-parameters.txt.

Tip: Obtaining Kernel Documentation

Install the kernel-source package to view the kernel documentation.

There are other ACPI-related kernel parameters that can be entered at the boot prompt prior to booting for installation:

Once you have determined the right parameter combination, YaST automatically writes them to the boot loader configuration to make sure that the system boots properly next time.

If unexplainable errors occur when the kernel is loaded or during the installation, select Memory Test in the boot menu to check the memory. If Memory Test returns an error, it is usually a hardware error.

After you insert the medium into your drive and reboot your machine, the installation screen comes up, but after you select Installation, the graphical installer does not start.

There are several ways to deal with this situation:

You inserted the medium into the drive, the BIOS routines are finished, but the system does not start with the graphical boot screen. Instead it launches a very minimalist text-based interface. This may happen on any machine not providing sufficient graphics memory for rendering a graphical boot screen.

Although the text boot screen looks minimalist, it provides nearly the same functionality as the graphical one:

For more information about log files that are created during installation, see Section 41.5, “Gathering Information during the Installation”.

If the hardware is functioning properly, it is possible that the boot loader is corrupted and Linux cannot start on the machine. In this case, it is necessary to repair the boot loader. To do so, you need to start the Rescue System as described in Section 42.6.2, “Using the Rescue System” and follow the instructions in Section 42.6.2.4, “Modifying and Re-installing the Boot Loader”.

Alternatively, you can use the Rescue System to fix the boot loader as follows. Boot your machine from the installation media. In the boot screen, choose More › Boot Linux System. Select the disk containing the installed system and kernel with the default kernel options.

When the system is booted, start YaST and switch to System › Boot Loader. Make sure that the Write generic Boot Code to MBR option is enabled, and press OK. This fixes the corrupted boot loader by overwriting it, or installs the boot loader if it is missing.

Other reasons for the machine not booting may be BIOS-related:

This behavior typically occurs after a failed kernel upgrade and it is known as a kernel panic because of the type of error on the system console that sometimes can be seen at the final stage of the process. If, in fact, the machine has just been rebooted following a software update, the immediate goal is to reboot it using the old, proven version of the Linux kernel and associated files. This can be done in the GRUB 2 boot loader screen during the boot process as follows:

If this does not fix the problem, boot the computer using the installation media. After the machine has booted, continue with Step 3.

If the machine starts, but does not boot into the graphical login manager, anticipate problems either with the choice of the default systemd target or the configuration of the X Window System. To check the current systemd default target run the command sudo systemctl get-default. If the value returned is not graphical.target, run the command sudo systemctl isolate graphical.target. If the graphical login screen starts, log in and start YaST › System › Services Manager and set the Default System Target to Graphical Interface. From now on the system should boot into the graphical login screen.

If the graphical login screen does not start even if having booted or switched to the graphical target, your desktop or X Window software is probably misconfigured or corrupted. Examine the log files at /var/log/Xorg.*.log for detailed messages from the X server as it attempted to start. If the desktop fails during start, it may log error messages to the system journal that can be queried with the command journalctl (see Chapter 16, journalctl: Query the systemd Journal for more information). If these error messages hint at a configuration problem in the X server, try to fix these issues. If the graphical system still does not come up, consider reinstalling the graphical desktop.

If a btrfs root partition becomes corrupted, try the following options:

If the root partition becomes corrupted, use the parameter forcefsck on the boot prompt. This passes the option -f (force) to the fsck command.

This often occurs when the system is configured to use network authentication or directory services and cannot retrieve results from its configured servers. The root user is the only local user that can still log in to these machines. The following are common reasons a machine appears functional but cannot process logins correctly:

In cases that do not involve external network problems, the solution is to log in as root and repair the configuration. If you cannot log in to the running system, reboot it into the rescue mode as outlined in Procedure 13.3, “Entering rescue mode”.

This is by far the most common problem users encounter, because there are many reasons this can occur. Depending on whether you use local user management and authentication or network authentication, login failures occur for different reasons.

Local user management can fail for the following reasons:

To locate the reason for a local login failure, proceed as follows:

In the following, common reasons a network authentication for a particular user may fail on a specific machine are listed:

To locate the cause of the login failures with network authentication, proceed as follows:

It is recommended to use an encrypted home partition for laptops. If you cannot log in to your laptop, the reason might be that your partition could not be unlocked.

During the boot time, you need to enter the passphrase to unlock your encrypted partition. If you do not enter it, the boot process continues, leaving the partition locked.

To unlock your encrypted partition, proceed as follows:

If you have a problem with network connectivity, narrow it down as described in Procedure 42.6, “How to Identify Network Problems”. If NetworkManager seems to be the culprit, proceed as follows to get logs providing hints on why NetworkManager fails:

For more information about NetworkManager, refer to Chapter 38, Using NetworkManager.

Sometimes you need to perform a backup from an entire partition or even hard disk. Linux comes with the dd tool which can create an exact copy of your disk. Combined with gzip you save some space.

If you only need to back up a partition, replace the SOURCE placeholder with your respective partition. In this case, your image file can lie on the same hard disk, but on a different partition.

There are several reasons a system could fail to come up and run properly. A corrupted file system following a system crash, corrupted configuration files, or a corrupted boot loader configuration are the most common ones.

To help you to resolve these situations, SUSE Linux Enterprise Server contains a rescue system that you can boot. The rescue system is a small Linux system that can be loaded into a RAM disk and mounted as root file system, allowing you to access your Linux partitions from the outside. Using the rescue system, you can recover or modify any important aspect of your system.

The rescue system can be loaded from various sources and locations. The simplest option is to boot the rescue system from the original installation medium.

Note: IBM IBM Z Starting the Rescue System

On IBM IBM Z the installation system can be used for rescue purposes. To start the rescue system follow the instructions in Section 42.7, “IBM IBM Z: Using initrd as a Rescue System”.

Once you have entered the rescue system, you can use the virtual consoles that can be reached with Alt–F1 to Alt–F6.

A shell and other useful utilities, such as the mount program, are available in the /bin directory. The /sbin directory contains important file and network utilities for reviewing and repairing the file system. This directory also contains the most important binaries for system maintenance, such as fdisk, mkfs, mkswap, mount, and shutdown, ip and ss for maintaining the network. The directory /usr/bin contains the vi editor, find, less, and SSH.

To see the system messages, either use the command dmesg or view the system log with journalctl.

42.6.2.2 Repairing and checking file systems #

 

Generally, file systems cannot be repaired on a running system. If you encounter serious problems, you may not even be able to mount your root file system and the system boot may end with a “kernel panic”. In this case, the only way is to repair the system from the outside. The system contains the fsck utility to check and repair multiple file system types, such as ext2, ext3, ext4, msdos, and vfat. Use the -t option to specify which file system to check.

The following command checks all ext4 file systems found in the /etc/fstab specification:

tux > sudo fsck -t ext4 -A

Tip

For Btrfs, you can use the btrfs check command found in the btrfsprogs package.

Generally, file systems cannot be repaired on a running system. If you encounter serious problems, you may not even be able to mount your root file system and the system boot may end with a “kernel panic”. In this case, the only way is to repair the system from the outside. The system contains the fsck utility to check and repair multiple file system types, such as ext2, ext3, ext4, msdos, and vfat. Use the -t option to specify which file system to check.

The following command checks all ext4 file systems found in the /etc/fstab specification:

tux > sudo fsck -t ext4 -A

Tip

For Btrfs, you can use the btrfs check command found in the btrfsprogs package.

Find topics about the Btrfs file system in the following places:

• The Storage Administration Guide includes https://documentation.suse.com/sles/html/SLES-all/cha-filesystems.html#sec-filesystems-major-btrfs and https://documentation.suse.com/sles/15-SP5/html/SLES-all/cha-resize-fs.html#sec-resize-fs-btrfs sections.

• The following article https://www.suse.com/support/kb/doc/?id=000018769 describes how to recover from Btrfs errors.

• The following article includes links to multiple Btrfs related topics https://www.suse.com/support/kb/doc/?id=000018779.

• The man 8 btrfs-check man page details all options of the btrfs check command.

42.6.2.3 Accessing the Installed System #

 

If you need to access the installed system from the rescue system, you need to do this in a change root environment. For example, to modify the boot loader configuration, or to execute a hardware configuration utility.

To set up a change root environment based on the installed system, proceed as follows:

1. 

   Tip: Import LVM Volume Groups

   If you are using an LVM setup (refer to Part II, “Logical Volumes (LVM)” for more general details), import all existing volume groups in order to be able to find and mount the device(s):

   rootvgimport -a

   Run lsblk to check which node corresponds to the root partition. It is /dev/sda2 in our example:

   lsblk
   NAME        MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
   sda           8:0    0 149,1G  0 disk
   ├─sda1        8:1    0     2G  0 part  [SWAP]
   ├─sda2        8:2    0    20G  0 part  /
   └─sda3        8:3    0   127G  0 part
     └─cr_home 254:0    0   127G  0 crypt /home

2. Mount the root partition from the installed system:

   mount /dev/sda2 /mnt

3. Mount /proc, /dev, and /sys partitions:

   mount -t proc none /mnt/proc
   mount --rbind /dev /mnt/dev
   mount --rbind /sys /mnt/sys

4. Now you can “change root” into the new environment, keeping the bash shell:

   chroot /mnt /bin/bash

5. Finally, mount the remaining partitions from the installed system:

   mount -a

6. Now you have access to the installed system. Before rebooting the system, unmount the partitions with umount -a and leave the “change root” environment with exit.

Warning: Limitations

Although you have full access to the files and applications of the installed system, there are some limitations. The kernel that is running is the one that was booted with the rescue system, not with the change root environment. It only supports essential hardware and it is not possible to add kernel modules from the installed system unless the kernel versions are identical. Always check the version of the currently running (rescue) kernel with uname -r and then find out if a matching subdirectory exists in the /lib/modules directory in the change root environment. If yes, you can use the installed modules, otherwise you need to supply their correct versions on other media, such as a flash disk. Most often the rescue kernel version differs from the installed one — then you cannot simply access a sound card, for example. It is also not possible to start a graphical user interface.

Also note that you leave the “change root” environment when you switch the console with Alt–F1 to Alt–F6.

42.6.2.5 Fixing Kernel Installation #

 

A kernel update may introduce a new bug which can impact the operation of your system. For example a driver for a piece of hardware in your system may be faulty, which prevents you from accessing and using it. In this case, revert to the last working kernel (if available on the system) or install the original kernel from the installation media.

Tip: How to Keep Last Kernels after Update

To prevent failures to boot after a faulty kernel update, use the kernel multiversion feature and tell libzypp which kernels you want to keep after the update.

For example to always keep the last two kernels and the currently running one, add

multiversion.kernels = latest,latest-1,running

to the /etc/zypp/zypp.conf file. See 15장 여러 커널 버전 설치 for more information.

A similar case is when you need to re-install or update a broken driver for a device not supported by SUSE Linux Enterprise Server. For example when a hardware vendor uses a specific device, such as a hardware RAID controller, which needs a binary driver to be recognized by the operating system. The vendor typically releases a Driver Update Disk (DUD) with the fixed or updated version of the required driver.

In both cases you need to access the installed system in the rescue mode and fix the kernel related problem, otherwise the system may fail to boot correctly:

1. Boot from the SUSE Linux Enterprise Server installation media.

2. If you are recovering after a faulty kernel update, skip this step. If you need to use a driver update disk (DUD), press F6 to load the driver update after the boot menu appears, and choose the path or URL to the driver update and confirm with Yes.

3. Choose Rescue System from the boot menu and press Enter. If you chose to use DUD, you will be asked to specify where the driver update is stored.

4. Enter root at the Rescue: prompt. A password is not required.

5. Manually mount the target system and “change root” into the new environment. For more information, see Section 42.6.2.3, “Accessing the Installed System”.

6. If using DUD, install/re-install/update the faulty device driver package. Always make sure the installed kernel version exactly matches the version of the driver you are installing.

   If fixing faulty kernel update installation, you can install the original kernel from the installation media with the following procedure.

   1. Identify your DVD device with hwinfo --cdrom and mount it with mount /dev/sr0 /mnt.

   2. Navigate to the directory where your kernel files are stored on the DVD, for example cd /mnt/suse/x86_64/.

   3. Install required kernel-*, kernel-*-base, and kernel-*-extra packages of your flavor with the rpm -i command.

7. Update configuration files and reinitialize the boot loader if needed. For more information, see Section 42.6.2.4, “Modifying and Re-installing the Boot Loader”.

8. Remove any bootable media from the system drive and reboot.