File System

Some notes on working with the linux file system

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• Create Swap File
• Detect new disk size without reboot
• Re-Scan SCSI Bus After Adding New Disk
• Full Disk Restore Checklist
  • Update fstab
  • Generate new initrd
  • Update grub config
  • Update network settings
  • Install grub

Create Swap File

fallocate -l 4G /swap
chmod 600 /swap
mkswap /swap
swapon /swap

/etc/fstab:

/swap swap swap defaults 0 0

Detect new disk size without reboot

Tested on a VM:

echo 1 >/sys/class/scsi_device/<Disk ID>/device/rescan

You can check in /dev/disk/by-path/ for the correct ID

Re-Scan SCSI Bus After Adding New Disk

echo "- - -" > /sys/class/scsi_host/hostX/scan

Full Disk Restore Checklist

For when you're using a backup system that doesn't handle the boot configuration, grub, etc.

Update fstab

Grab the new UUID of the disks by running blkid
Edit /etc/fstab and replace any /dev/sdX or UUID= entries with the new UUID=xxxxxxx

Generate new initrd

For Centos 6, run dracut -f
You can also target a specific version of the kernel: dracut -f </boot/filename.img> <kernel.version.x86_64>
Reference here (opens new window)

Update grub config

Different methods used depending on flavour of linux. For Centos 6, you can just edit /etc/grub.conf
Replace any UUID references with your new ones

Update network settings

Update the MAC for the network interfaces if this is a different machine. Edit the file at /etc/udev/rules.d/70-persistent-net.rules

Install grub

For Centos 6, run grub-install