Linux Tipps und Tricks

Tipps und Tricks

Hard reboot

This is the hard way to kick your kernel into void. No filesystem sync is done, just and ugly fast direkt reboot! You should never do this...

# echo 1 > /proc/sys/kernel/sysrq
# echo b > /proc/sysrq-trigger

First line enables sysrq, second line sends the reboot request.

For more look at kernel.org!

Scan all SCSI buses for new devices

# for i in  /sys/class/scsi_host/host*/scan ; do echo "- - -" > $i ; done

Rescan a device (for example after changing a VMDK size)

# echo 1 > /sys/class/block/${device}/device/rescan

This is for device sda after changing the VMDK from 20GB to 25GB:

# echo $[ 512 * $(cat /sys/block/sda/size) / 1024 / 1024 / 1024 ]
20
# echo 1 > /sys/class/block/sda/device/rescan
# echo $[ 512 * $(cat /sys/block/sda/size) / 1024 / 1024 / 1024 ]
25

Remove a SCSI-device

Let us say we want to remove /dev/sdb.

Be careful! Like in this example the lowest SCSI-ID is not always the lowest device name! Check it with lsscsi from the Ubuntu package lsscsi:

# lsscsi
[2:0:0:0]    cd/dvd  NECVMWar VMware SATA CD00 1.00  /dev/sr0
[32:0:0:0]   disk    VMware   Virtual disk     1.0   /dev/sdb
[32:0:1:0]   disk    VMware   Virtual disk     1.0   /dev/sda

Then check it is not longer in use:

1. mount
2. pvs
3. zpool status
4. etc.

Then delete it:

# echo 1 >  /sys/bus/scsi/drivers/sd/32\:0\:0\:0/delete

The 32:0:0:0 is the number reported from the lsscsi above.

Et voila:

# lsscsi
[2:0:0:0]    cd/dvd  NECVMWar VMware SATA CD00 1.00  /dev/sr0
[32:0:1:0]   disk    VMware   Virtual disk     1.0   /dev/sda

Copy a GPT partition table

Copy partition table of sdX to sdY:

# sgdisk /dev/sdX --replicate=/dev/sdY 
# sgdisk --randomize-guids /dev/sdY

       -R, --replicate=second_device_filename
              Replicate  the  main device's partition table on the specified second device.  Note that the replicated partition table is an exact
              copy, including all GUIDs; if the device should have its own unique GUIDs, you should use the -G option on the new disk.

       -G, --randomize-guids
              Randomize the disk's GUID and all partitions' unique GUIDs (but not their partition type code GUIDs). This  function  may  be  used
              after cloning a disk in order to render all GUIDs once again unique.

Resize a GPT partition

The partition was resized in VMWare from ~6GB to ~50GB.

In the VM I did Remove a SCSI-device for the resized device and then Scan all SCSI buses for new devices after that parted saw the new size.

Correct the GPT partition table

root@mariadb:~# parted /dev/sdb                                
GNU Parted 3.2
Using /dev/sdb
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p                                                                
Warning: Not all of the space available to /dev/sdb appears to be used, you can fix the GPT to use all of the space (an extra 92274688 blocks) or continue with the
current setting? 
Fix/Ignore? F                                    <-- ! choose F                         
Model: VMware Virtual disk (scsi)
Disk /dev/sdb: 53,7GB                            <-- ! the new size is reported now
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name  Flags
 1      1049kB  6442MB  6441MB  zfs

Resize the partition

root@mariadb:~# parted /dev/sdb
GNU Parted 3.2
Using /dev/sdb
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p                                                                
Model: VMware Virtual disk (scsi)
Disk /dev/sdb: 53,7GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name  Flags
 1      1049kB  6442MB  6441MB  zfs

(parted) resizepart 1                                                     
End?  [6442MB]? 53,7GB                         <-- ! Put new size here                           
(parted) p                                     <-- ! Control if it worked                           
Model: VMware Virtual disk (scsi)
Disk /dev/sdb: 53,7GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name  Flags
 1      1049kB  53,7GB  53,7GB  zfs

(parted) q                                                                
Information: You may need to update /etc/fstab.

Optional: Resize the ZPool in it

Check the actual values:

root@mariadb:~# zpool list MYSQL-DATA
NAME         SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
MYSQL-DATA  5,97G   994M  5,00G       44G    47%    16%  1.00x  ONLINE  -
root@mariadb:~# zpool get autoexpand MYSQL-DATA
NAME        PROPERTY    VALUE   SOURCE
MYSQL-DATA  autoexpand  off     default

Now inform ZPool to grow to the end of the partition. Set autoexpand to on:

root@mariadb:~# zpool set autoexpand=on MYSQL-DATA

Send an online to the already onlined device to force a recheck in the ZPool to resize it without export/import:

root@mariadb:~# zpool online  MYSQL-DATA /dev/sdb1

Et voila:

root@mariadb:~# zpool list MYSQL-DATA
NAME         SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
MYSQL-DATA  50,0G   994M  49,0G         -     5%     1%  1.00x  ONLINE  -
rpool       19,9G  3,36G  16,5G         -    19%    16%  1.00x  ONLINE  -

Set autoexpand to off if you want prevent to autoexpand if partition grows:

root@mariadb:~# zpool set autoexpand=off MYSQL-DATA