# RHEL7升级后磁盘设备label识别错误处理 从我厂自制的OS 7u2升级转换到CentOS 7u2操作系统，总是发生内核一旦升级，就无法正常启动。这个问题困扰了我很久，往往退而求其次，避开升级内核。但是，伪处女座，不能忍啊！ 从带外检查启动输出显示 ``` Starting udev Kernel Device Manager... [ OK ] Started udev Kernel Device Manager. Starting udev Coldplug all Devices... Mounting Configuration File System... [ OK ] Mounted Configuration File System. [ OK ] Started udev Coldplug all Devices. [ OK ] Reached target System Initialization. [ 5.378473] megasas:IOC Init cmd success Starting drac[ OK ] Started Show Plymouth Boot Screen. [ OK ] Reached target Paths. [ OK ] Reached target Basic System. [ 5.425533] megasas: INIT adapter done [ OK ] Found device P[ 5.843292] systemd-fsck[522]: Failed to detect devic/ ERC_H710P /. [ 5.852940] systemd[1]: Failed to start File System Check on /dev/disk/by-l. Starting[ 5.862951] systemd[1]: Dependency failed for /sysroot. File System Che[ 5.870309] systemd[1]: Dependency failed for Initrd Root Fi. ck on /dev/disk/[ 5.879141] systemd[1]: Dependency failed for Reload Configu. by-label/\x2f... [FAILED] Failed to start File System Check on /dev/disk/by-label/\x2f. See 'systemctl status sys Generating "/run/initramfs/rdsosreport.txt" Entering emergency mode. Exit the shell to continue. Type "journalctl" to view system logs. You might want to save "/run/initramfs/rdsosreport.txt" to a USB stick or /boot after mounting them and attach it to a bug report. ``` 报错显示和磁盘的label有关，也就是升级以后，设备文件无法找到原先按照`label`标记的磁盘设备。我遇到过以往升级后，磁盘设备完全是被为UUID的情况，所以推测有可能类似情况又发生了。 * 切换到磁盘操作系统 ``` mkdir /mnt mount /dev/sda2 /mnt mount /dev/sda1 /mnt/boot mount -t proc proc /mnt/proc mount --rbind /sys /mnt/sys mount --make-rslave /mnt/sys mount --rbind /dev /mnt/dev mount --make-rslave /mnt/dev chroot /mnt /bin/bash source /etc/profile ``` * 检查系统设备 ``` cd /dev/disk/by-label ls -lh ``` 显示输出 ``` total 0 lrwxrwxrwx 1 root 0 10 Jul 16 10:52 SWAP -> ../../sda3 lrwxrwxrwx 1 root 0 10 Jul 16 10:52 \x2f -> ../../sda2 lrwxrwxrwx 1 root 0 10 Jul 16 10:52 \x2fboot -> ../../sda1 ``` 看来是设备文件`by-label`识别的时候原先的`/`符号被识别成了`\x2f` - 通过挂载`/dev/sda2`(挂载命令 `mkdir /mnt;mount /dev/sda2 /mnt`)检查这个磁盘设备下的文件 `etc/fstab` 可以看到，原先设置是 ``` LABEL=/boot /boot ext4 defaults 1 2 LABEL=/ / ext4 defaults 1 1 LABEL=SWAP swap swap defaults 0 0 ``` 凡是带`/`开头的符号都被识别成了`\x2f`，所以需要修改磁盘挂载。 可以采用以下方法之一： * 使用旧版本内核启动，然后从新对磁盘分区进行`label`，去除掉不兼容的`/`符号。然后再重启到新内核 * 直接修改`etc/fstab`，将`LABEL=`识别磁盘的方式更改为使用UUID识别方式 ## `label`标记分区 参考 [Label a Linux Partition](http://www.cyberciti.biz/faq/linux-partition-howto-set-labels/) 使用 `e2label` 命令 * 显示分区标记 ``` cd /sbin ./e2label /dev/sda1 ``` 输出显示 ``` /boot ``` * 修改分区标记 ``` ./e2label /dev/sda1 BOOT ``` 同样再修改 `/dev/sda2` ``` ./e2label /dev/sda2 ROOT ``` * 修改`etc/fstab`配置如下 ``` LABEL=BOOT /boot ext4 defaults 1 2 LABEL=ROOT / ext4 defaults 1 1 LABEL=SWAP swap swap defaults 0 0 ``` 但是很奇怪，重启依然没有找到`by-label`设备。 汗，忘记修改 grub 启动中的配置了！原先的配置中还遗留着对`/dev/disk/by-label/\x2f`的引用！ 编辑 `/mnt/boot/grub2/grub.cfg` 可以看到，这个文件不是直接编辑的，是通过编辑模板`/etc/grub.d`目录下模板和 `/etc/default/grub`后，然后通过`grub2-mkconfig`生成的。在斌即过`/etc/fstab`之后（更换`label`或者从`label`转换到`uuid`或相反），需要执行一次`grub2-mkconfig`来生成新的配置文件。 > 检查 `/boot/grub2/grub.cfg` 可以看到如下配置显示是采用`root=LABEL=/` ``` #grep "root=LABEL" grub.cfg linux16 /vmlinuz-0-rescue-0b784259b076423083282fb71ecc7fa9 root=LABEL=/ ro crashkernel=auto vconsole.font=latarcyrheb-sun16 vconsole.keymap=us biosdevname=0 ipv6.disable=1 console=tty0 console=ttyS0,115200 scsi_mod.scan=sync LANG=en_US.UTF-8 linux16 /vmlinuz-3.10.0-327.22.2.el7.x86_64 root=LABEL=/ ro crashkernel=auto vconsole.font=latarcyrheb-sun16 vconsole.keymap=us biosdevname=0 ipv6.disable=1 console=tty0 console=ttyS0,115200 scsi_mod.scan=sync LANG=en_US.UTF-8 ``` 上述两行就是新安装内核自动添加按照磁盘`LABEL=/`来挂载启动盘。虽然后面订正了`/etc/fstab`，但是`grub.cfg`没有订正。 ``` cp grub.cfg grub.cfg.bak grub2-mkconfig ``` 不过，再次启动，依然存在问题，显示 ``` [ 5.468314] megasas: INIT adapter done [ TIME 94.982368] systemd[1]: Timed out waiting for device dev-disk-by\x2dlabel-\x5cx2f.device. 0m] Timed out wa[ 94.982696] systemd[1]: Dependency failed for /sysroot. iting for device dev-disk-by\x2d[ 95.000182] systemd[1]: Dependency failed for Initrd Root File System. label-\x5cx2f.de[ 95.010574] systemd[1]: Dependency failed for Reload Configuration from the Real Root. vice. [[ 95.020962] systemd[1]: Dependency failed for File System Check on /dev/disk/by-label/\x2f. DEPEND] Dependency failed foWarning: /dev/disk/by-label/x2f does not exist Generating "/run/initramfs/rdsosreport.txt" Entering emergency mode. Exit the shell to continue. Type "journalctl" to view system logs. You might want to save "/run/initramfs/rdsosreport.txt" to a USB stick or /boot after mounting them and attach it to a bug report. ... [ 128.769627] dracut-initqueue[466]: Warning: dracut-initqueue timeout - starting timeout scripts [ 129.292098] dracut-initqueue[466]: Warning: dracut-initqueue timeout - starting timeout scripts ... [ 189.812708] dracut-initqueue[466]: Warning: Could not boot. [ 189.815089] dracut-initqueue[466]: Warning: /dev/disk/by-label/x2f does not exist [ 189.826322] dracut-initqueue[466]: Failed to start dracut-emergency.service: Transaction is destructive. [ 189.829207] dracut-initqueue[466]: Warning: Not all disks have been found. [ 189.829534] dracut-initqueue[466]: Warning: You might want to regenerate your initramfs. ``` **这步不需要**：按照提示我尝试创建`initramfs`文件来修正磁盘启动 - 对于RHEL/CentOS 6/7 ，需要使用 `dracut` 工具(不过这个步骤看来无效，应该还是需要手工订正`/boot/grub2/grub.cfg`) ``` cd /boot cp initramfs-3.10.0-327.22.2.el7.x86_64.img initramfs-3.10.0-327.22.2.el7.x86_64.img.bak dracut -f /boot/initramfs-3.10.0-327.22.2.el7.x86_64.img 3.10.0-327.22.2.el7.x86_64 ``` > 如果是ubuntu/debian，则参考 [UsingUUID](https://help.ubuntu.com/community/UsingUUID)，编辑 `/etc/initramfs-tools/conf.d/resume` 将这个文件中的UUID或者label订正成正确的值并保存。再执行命令 `sudo update-initramfs -u` 不过，执行之后依然没有解决系统启动后还是在寻找`/dev/disk/by-label/x2f`，报错依然相同。我本来以为`grub2-mkconfig`命令会自动按照`/etc/fstab`中设置来创建`/boot/grub2/grub.cfg`，但是发现执行后`grub.cfg`中依然是保留了原来的`root=LABEL=/`，所以需要手工订正这个配置文件，将 `root=LABEL=/` 修改成 `root=LABEL=ROOT`。 果然，最终是手工通过修正`/boot/grub2/grub.cfg`来解决启动时候启动分区识别 ## UUID 除了上述通过`e2label`修正磁盘设备的`label`，另一种方法是使用磁盘设备的UUID。参考 [How To Use UUID To Mount Partitions / Volumes Under Ubuntu Linux](http://www.cyberciti.biz/faq/linux-finding-using-uuids-to-update-fstab/)： * 检查磁盘UUID ``` cd /sbin ./blkid ``` 显示输出 ``` /dev/sda1: LABEL="BOOT" UUID="ac7453fb-aa2a-4bc2-9114-78bd9fb62cb5" TYPE="ext4" /dev/sda2: LABEL="ROOT" UUID="37d96a70-ae3f-4591-91de-e29145faad8d" TYPE="ext4" /dev/sda3: LABEL="SWAP" UUID="23e9c8b6-22fd-46b4-8e2f-78eb33127dcd" TYPE="swap" ``` * 修改`etc/fstab`如下 ``` UUID=ac7453fb-aa2a-4bc2-9114-78bd9fb62cb5 /boot ext4 defaults 1 2 UUID=37d96a70-ae3f-4591-91de-e29145faad8d / ext4 defaults 1 1 UUID=23e9c8b6-22fd-46b4-8e2f-78eb33127dcd swap swap defaults 0 0 ``` * 同样，需要手工修改 `/boot/grub2/grub.cfg` 将原先启动参数 `root=LABEL=/` 修改成 `root=UUID=37d96a70-ae3f-4591-91de-e29145faad8d` ## 小结 当修改磁盘的DISK label时，需要修改2个位置： * `/etc/fstab` 对应更改`LABEL`或者`UUID` * 修改`/boot/grub2/grub.cfg`将启动参数中`root=LABEL=/`修改成都应的`LABEL`或者`UUID` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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