# Boot Issues - select a kernel version to run in recovery mode from GRUB bootloader menu ![[images/recovery.png]] - fs is typically in read-only while in recovery mode - `mount -o remount,rw / && mount --all` to remount root fs in rw mode and others - `fsck` to run fs check utility - typically run fsck on unmounted disks; to unmount a fs `sudo umount /` - `sudo fdisk -l` to list disk partitions - `sudo grub-install --boot-directory=/dev/sda` to reinstall grub - review `/var/boot.log` and `dmesg` - important to have a live boot USB handy to boot from to diagnosis issues with disk # Storage Issues - common storage commands - `mount` to list mounted partitions and mount partitions ![[images/Pasted image 20250801194036.png]] - `umount` to unmount partitions - `lsblk` shows block devices ![[images/Pasted image 20250717201930.png]] - `fdisk` to view and manage partitions - `sudo fdisk -l /dev/sda` shows details for sda disk - `sudo fsck -vy` to find and automatically repair disk errors - `sudo fstrim` to remove unused blocks - `partprobe` informs kernel of partition changes w/o rebooting - `df -h` shows disk free in human readable format ![[images/Pasted image 20250731094336.png]] - `du -d 1 /target_dir` shows space used by sub-directories that are one level below the target directory ![[images/Pasted image 20250731094750.png]] - `iostat [options] [interval] [count]` to troubleshoot disk I/O issues - also try `iotop`,`ioping`, and `fio` - `sudo fsck /dev/sda1` runs fs check on sda1 partition - `cat /etc/fstab` shows entries for persistent mount points - change fs size - `sudo fdisk -l` to show disks and associated partitions - `sudo umount /dev/sdb1` to unmount sdb1 partition - `sudo e2fsck -f /dev/sdb1` to run fs check on sdb1 partition - `resize2fs /dev/sdb1 1200M` to resize sdb1 partition to 1.2G - manage swap space - swap is used when physical RAM is exhausted - least used blocks are moved to swap (memory to disk) - swap can be a file or a partition - `free -m` shows memory and swap space ![[images/Pasted image 20250731095829.png]] - `sudo fdisk -l` shows disks and associated partitions - `sudo fdisk /dev/sdd` to create a fresh partition on sdd - `sudo mkswap /dev/sdd1` to create swapspace on fresh sdd1 partition - `sudo swapon -v /dev/sdd1` to enable swapspace - `free -m` shows newly created and enabled swapspace