Device

Updated: 2020-12-29

udev

udev (userspace /dev)

/dev is static, udev is for plugable devices running in userspace.

To be able to deal with peripheral devices that are hotplug-capable in a user-friendly way, a part of handling all of these hotplug-capable hardware devices was handed over from the kernel to a daemon running in user-space. Running in user space serves security and stability purposes.

udev primarily manages device nodes in the /dev directory, Unlike traditional Unix systems, where the device nodes in the /dev directory have been a static set of files, the Linux udev device manager dynamically provides only the nodes for the devices actually present on a system.

$ ps -e | grep udevd
  304 ?        00:00:00 systemd-udevd



$ ps -e | grep systemd
  304 ?        00:00:00 systemd-udevd
 1317 ?        00:00:00 systemd-logind

Check attacked EBS(sda/sdf may be renamed to xvda/xvdf)

$ sudo fdisk -l
Disk /dev/xvda1: 8589 MB, 8589934592 bytes
255 heads, 63 sectors/track, 1044 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/xvda1 doesn't contain a valid partition table

Disk /dev/xvdf: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Format EBS

$ sudo mkfs -t ext4 /dev/xvdf

Edit fstab and reboot

$ vi /etc/fstab

or manually mount

# mkdir /mnt/tmp
# mount /dev/xvdf /mnt/tmp
# umount /dev/xvdf

XFS

$ sudo apt-get install xfsprogs
$ sudo mkfs.xfs /dev/sdf
$ sudo mount -t xfs -o defaults /dev/sdf /var/www

Mount / Umount

Assume a device is added as /mnt/vdc. Create new folder as /dev/vdc

$ sudo mkdir /dev/vdc

Edit /etc/fstab.

# <file system> <mount point>   <type>  <options>       <dump>  <pass>
/dev/vdc        /mnt/vdc        auto    defaults        0       0

Mount all

$ sudo mount -a

Check by df

$ df
Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/vdc           65390      36     65354   1% /mnt/vdc

To remount

$ mount -o remount /dev/vdc

Mount disk

$ mount /dev/sdf /mnt/workspace

umount: it seems [device] is mounted multiple times

Error:

$ umount /dev/[device]
umount: it seems /dev/<device> is mounted multiple times

Solution: use sudo

$ sudo umount /dev/[device]

Format a Device

Use mkfs.ext2, mkfs.ext3, mkfs.ext4 etc

$ sudo mkfs.ext3 /dev/<device>

Check FS

# df -hT | awk '{print $1,$2,$NF}' | grep "^/dev"
/dev/sda3 ext4 /
/dev/sda2 ext2 /boot
/dev/sda6 ext4 /tmp
/dev/sdb1 ext4 /data1
/dev/sdc1 ext4 /data2
/dev/sdd1 ext4 /data3

cmd

  • mkfs
  • mke2fs
  • tune2fs
  • mkswap

mke2fs -F -j /dev/sdh mkdir /ebs mount /dev/sdh /ebs

copy to ebs:

dd bs=65536 if=/dev/sda1 of=/dev/sdh
fsck /dev/sdh

check

df -h

fsck /dev/sdh