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271 lines
9.1 KiB
Text
= How to debug Dracut problems
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*Foreword*
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If you are experiencing a problem with system initialization due to
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Dracut, please see the link:Bugs/Common[common bugs] document before
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filing a bug. Some easy configuration tweaks that fix a wide range of
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issues may be listed there. If the problem you are seeing is not listed
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there or none of the workarounds seem to help, please consider filing a
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bug to help us make Fedora run better on your hardware.
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Be prepared to include some information (logs) about your system as
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well. These should be complete (no snippets please), not in an archive,
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uncompressed, with MIME type set as text/plain.
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[[identifying-your-problem-area]]
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== Identifying your problem area
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1. Remove `rhgb` and `quiet` from the kernel command line
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2. Add `rd.shell` to the kernel command line. This will present a shell
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in case dracut is unable to locate your root device
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3. Add `rd.shell rd.debug log_buf_len=1M` to the kernel command line so
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that dracut shell commands are printed as they are executed
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4. Inspect the system logs:
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....
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# less /run/initramfs/rdsosreport.txt
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# journalctl -a
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# dmesg
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# less /run/initramfs/init.log
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....
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[[information-to-include-in-your-report]]
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== Information to include in your report
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[[all-bug-reports]]
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=== All bug reports
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In all cases, the following should be mentioned and attached to your bug
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report:
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* The exact kernel command-line used. Typically from the bootloader
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configuration file (e.g. `/etc/grub.conf`) or from `/proc/cmdline`
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* A copy of your disk partition information from `/etc/fstab`
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* A device listing from device-mapper. This can be obtained by running
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the command `dmsetup ls -- tree`
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* A list of block device attributes including vol_id compatible mode.
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This can be obtained by running the commands `blkid` and `blkid -o udev`
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* Turn on dracut debugging (see link:How_to_debug_Dracut_problems#Debugging[the 'debugging dracut'
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section]), and attach all relevant information from the boot log. This
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can be obtained by running the command `dmesg|grep dracut`
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* If you use a dracut configuration file, please include `/etc/dracut.conf`
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[[logical-volume-management-related-problems]]
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=== Logical Volume Management related problems
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As well as the information from
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link:How_to_debug_Dracut_problems#AllInfo[the 'all bug reports'
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section], include the following information:
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* Include physical volume information by running the command: `lvm pvdisplay`
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* Include volume group information by running the command: `lvm vgdisplay`
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* Include logical volume information by running the command: `lvm lvdisplay`
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[[software-raid-related-problems]]
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=== Software RAID related problems
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As well as the information from
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link:How_to_debug_Dracut_problems#AllInfo[the 'all bug reports'
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section], include the following information:
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* If using software RAID disk partitions, please include the output of `/proc/mdstat`
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[[network-root-device-related-problems]]
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Network root device related problems
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This section details information to include when experiencing problems
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on a system whose root device is located on a network attached volume
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(e.g. iSCSI, NFS or NBD). As well as the information from
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link:How_to_debug_Dracut_problems#AllInfo[the 'all bug reports'
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section], include the following information:
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* Please include the output of
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[[debugging-dracut]]
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== Debugging dracut
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[[configure-a-serial-console]]
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=== Configure a serial console
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Successfully debugging dracut will require some form of console logging
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during the system boot. This section documents configuring a serial
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console connection to record boot messages. To enable serial console
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output for both the kernel and the bootloader, follow the procedure
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below.
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1. Open the file `/etc/grub.conf` for editing. Below the line _timeout=5_, add the following:
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....
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serial --unit=0 --speed=9600
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terminal --timeout=5 serial console
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....
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2. Also in `/etc/grub.conf`, add the following boot arguments to the _kernel_ line:
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....
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console=tty0 console=ttyS0,9600
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....
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3. When finished, `/etc/grub.conf` should look similar to the example below:
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....
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default=0
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timeout=5
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serial --unit=0 --speed=9600
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terminal --timeout=5 serial console
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title Fedora (2.6.29.5-191.fc11.x86_64)
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root (hd0,0)
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kernel /vmlinuz-2.6.29.5-191.fc11.x86_64 ro root=/dev/mapper/vg_uc1-lv_root console=tty0 console=ttyS0,9600
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initrd /dracut-2.6.29.5-191.fc11.x86_64.img
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....
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More detailed information on how to configure the kernel for console
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output can be found at
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http://www.faqs.org/docs/Linux-HOWTO/Remote-Serial-Console-HOWTO.html#CONFIGURE-KERNEL[1].
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[[using-the-dracut-shell]]
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=== Using the dracut shell
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Dracut offers a shell for interactive debugging in the event dracut
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fails to locate your root filesystem. To enable the shell:
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1. Add the boot parameter `rd.shell` to your bootloader configuration
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file (e.g. `/etc/grub/conf`)
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2. Remove the boot arguments `rhgb` and `quiet`
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A sample `/etc/grub.conf` bootloader configuration file is listed below:
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....
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default=0
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timeout=5
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serial --unit=0 --speed=9600
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terminal --timeout=5 serial console
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title Fedora (2.6.29.5-191.fc11.x86_64)
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root (hd0,0)
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kernel /vmlinuz-2.6.29.5-191.fc11.x86_64 ro root=/dev/mapper/vg_uc1-lv_root console=tty0 rd.shell
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initrd /dracut-2.6.29.5-191.fc11.x86_64.img
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....
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If system boot fails, you will be dropped into a shell as seen in the
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example below:
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....
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No root device found
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Dropping to debug shell.
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sh: can't access tty; job control turned off
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#
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....
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Use this shell prompt to gather the information requested above (see
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link:How_to_debug_Dracut_problems#AllInfo[the 'all bug reports'
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section]).
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[[accessing-the-root-volume-from-the-dracut-shell]]
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=== Accessing the root volume from the dracut shell
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From the dracut debug shell, you can manually perform the task of
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locating and preparing your root volume for boot. The required steps
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will depend on how your root volume is configured. Common scenarios
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include:
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* A block device (e.g. `/dev/sda7`)
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* A LVM logical volume (e.g. `/dev/VolGroup00/LogVol00`)
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* An encrypted device (e.g. `/dev/mapper/luks-4d5972ea-901c-4584-bd75-1da802417d83`)
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* A network attached device (e.g. `netroot=iscsi:@192.168.0.4::3260::iqn.2009-02.org.fedoraproject:for.all`)
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The exact method for locating and preparing will vary. However, to
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continue with a successful boot, the objective is to locate your root
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volume and create a symlink `/dev/root` which points to the file system. For example, the following example demonstrates accessing and booting a root volume that is an encrypted LVM Logical volume.
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1. Inspect your partitions using `parted`:
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....
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# parted /dev/sda -s p
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Model: ATA HTS541060G9AT00 (scsi)
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Disk /dev/sda: 60.0GB
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Sector size (logical/physical): 512B/512B
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Partition Table: msdos
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Number Start End Size Type File system Flags
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1 32.3kB 10.8GB 107MB primary ext4 boot
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2 10.8GB 55.6GB 44.7GB logical lvm
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....
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2. You recall that your root volume was a LVM logical volume. Scan and
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activate any logical volumes:
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....
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# lvm vgscan
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# lvm vgchange -ay
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....
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3. You should see any logical volumes now using the command `blkid`:
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....
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# blkid
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/dev/sda1: UUID="3de247f3-5de4-4a44-afc5-1fe179750cf7" TYPE="ext4"
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/dev/sda2: UUID="Ek4dQw-cOtq-5MJu-OGRF-xz5k-O2l8-wdDj0I" TYPE="LVM2_member"
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/dev/mapper/linux-root: UUID="def0269e-424b-4752-acf3-1077bf96ad2c" TYPE="crypto_LUKS"
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/dev/mapper/linux-home: UUID="c69127c1-f153-4ea2-b58e-4cbfa9257c5e" TYPE="ext3"
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/dev/mapper/linux-swap: UUID="47b4d329-975c-4c08-b218-f9c9bf3635f1" TYPE="swap"
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....
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4. From the output above, you recall that your root volume exists on an
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encrypted block device. Following the guidance disk encryption guidance
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from the
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http://docs.fedoraproject.org/install-guide/f%7B%7BFedoraVersion%7D%7D/en-US/html/apcs04s04.html[
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Installation Guide], you unlock your encrypted root volume.
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....
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UUID=$(cryptsetup luksUUID /dev/mapper/linux-root)
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cryptsetup luksOpen /dev/mapper/linux-root luks-$UUID
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Enter passphrase for /dev/mapper/linux-root:
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Key slot 0 unlocked.
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....
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5. Next, make a symbolic link to the unlocked root volume
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....
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ln -s /dev/mapper/luks-$UUID /dev/root
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....
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6. With the root volume available, you may continue booting the system
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by exiting the dracut shell
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....
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exit
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....
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[[summary-of-dracut-kernel-command-line-options]]
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=== Summary of dracut kernel command line options
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A selection of the most common debugging related dracut options:
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==== `*rd.shell*`
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Drop to a shell, if the initramfs fails.
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==== `*rd.debug*`
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Set -x for the dracut shell.
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==== `*rd.break=[cmdline|pre-udev|pre-trigger|initqueue|pre-mount|mount|pre-pivot|cleanup]*`
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Drop the shell on defined breakpoint (use
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`egrep 'rd.?break' /usr/lib/dracut/modules.d/99base/init.sh` to find the
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breakpoints supported by your dracut version)
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==== `*rd.udev.info*`
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Set udev to loglevel info
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==== `*rd.udev.debug*`
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Set udev to loglevel debug
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See the `dracut.cmdline(7)`
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http://man7.org/linux/man-pages/man7/dracut.cmdline.7.html[man page] for
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the complete reference.
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Category:Debugging[D] Category:How_to[Category:How to]
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'''
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See a typo, something missing or out of date, or anything else which can be
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improved? Edit this document at https://pagure.io/fedora-docs/quick-docs.
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