---
title: linux disks
---

Note: Do not place `/usr` on a separate partition

## Mount a disk as read only / read write

```
mount -o remount,rw /path/to/mount
mount -o remount,ro /path/to/mount
```

## Find a new disk

This is useful if you've hot-added another disk, such as with VMWare

```
echo "- - -" > /sys/class/scsi_host/host0/scan
echo "- - -" > /sys/class/scsi_host/host1/scan
```

## LVM (Logical Volume Manager)

### To Create LVM

```
fdisk /dev/sda ->create 3 partitions + label to 8e
partprobe
fdisvk -l
pvcreate /dev/sda8 /dev/sda9
pvdisplay /dev/sda8
pvdisplay /dev/sda9
vgcreate vg0 /dev/sda8 /dev/sda9
vgdisplay
lvcreate -L +15g -n label_home /dev/vg00
lvcreate -l +100%FREE -n lv_name /dev/vg01
lvdisplay /dev/vg0/home1
lvcreate -L +300M -n /dev/vg0/var1
lvcreate -L +200GB -n oracle-export vg01
lvdisplay /dev/vg0/var1
mkfs.ext3 /dev/vg0/var1
mkfs.ext3 /dev/vg0/home1
mkdir /home1
mkdir /var1
mount /dev/vg0/home1 /home1
mount /dev/vg0/var1 /var1
cp /etc/a* /home1
cp /etc/b* /var1
vim /etc/fstab
mount -a
```

## LVM SNAPSHOT

```
lvcreate -L 200M -s -n lv2 /dev/llc/lv1
```

## To find the mapping of an LV

```
lvdisplay -m
```

## Extend PV

```
pvcreate /dev/sda999
pvdisplay
```

## To extend VG

```
vgextend vg00 /dev/sda999
vgdisplay vg00
```

## To reduce VG

```
vgreduce vg00 /dev/sda999
vgdisplay
```

## TO EXTEND LV (Adding 200M)

```
lvdisplay /dev/vg00/home
lvextend -L +200M /dev/vg00/home
lvextend -L +200M /dev/vg00/home /dev/sdc1
lvextend -l +100%FREE /dev/myvg/testlv
(optional) umount /home
resize2fs /dev/vg0/home
(optional) mount /home
```

## To reduce LVM (Reducing to 100M)

```
lvdisplay
umount /var1
e2fsck -f /dev/vg0/var1
resize2fs /dev/vg0/var1 100M
lvreduce -L 100M /dev/vg0/var1
mount /dev/vg0/var1 /var1
df -h
```

## TO REDUCE PV

pvremove /dev/sda10
pvdisplay

## REMOVE LVM

lvdisplay
umount /dev/vg0/home1
umount /dev/vg0/var1
vi /etc/fstab
lvremove /dev/vg0/home1
lvremove /dev/vg0/var1
lvdisplay
## REMOVE VG
vgdisplay
vgremove /dev/vg0
vgdisplay
## REMOVE PV
pvdisplay
pvremove /dev/sda9
pvremove /dev/sda8

## Label a filesystem

```
e2label /dev/sdb2 usbstroage
```

You can add to `/etc/fstab` "LABEL=labelname"

```
# <file system>           <mount point>    <type>  <options>            <dump>  <pass>
proc                      /proc            proc    nodev,noexec,nosuid  0       0
/dev/mapper/server-root   /                ext4    errors=remount-ro    0       1
UUID=nnnnnnnnnnnnnnnnnn  /boot  ext2  defaults        0       2
/dev/mapper/server-swap_1 none             swap    sw                   0       0
LABEL=seagate             /mnt/seagate     ntfs    defaults             0       2
LABEL=backup              /mnt/backup      ext4    ro,nosuid,noexec     0       2
LABEL=wd3tbgreen          /usr/local/var/crashplan/  ext4    nosuid,noexec        0       2
```

## Adding swap

```
swapon -s
lvcreate -L +16G -n /dev/vg00/swap2
mkswap /dev/mapper/vg00-swap2
vi /etc/fstab
swapon -a
swapon -s
```

## Which disk is an LV on

```
pvdisplay -m
lvdisplay -m
lvs -o +devices
lvs -a -o +devicesq
```

# From Shane

Linux rescue + lvm

Reboot. Edit grub config
On the end of the kernel line put "init=/bin/bash"
This mounts root as read only
mount -o remount,rw /
Make whatever changes are required (you might need to mount /proc)
Unmount anything mounted
mount -o remount,ro /
Afterwards "reboot" (not CTRL-D or it will lock up!!!)

----------------------------------------------------

To do a linux rescue boot (for resetting the root password for example) :

* Mount a redhat iso/dvd and boot off it
* Type "linux rescue" at the prompt
* Tell the OS not to mount the disks or connect the network interfaces
* When it boots type
* lvm vgscan
* lvm vgchange -a y
* The vg should be under /dev/[vg]/[lv] - which will likely link to /dev/mapper (eg /dev/mapper/vg00-root)
* Use this device to mount / fsck this volume as necessary

* Other commands - "lvm lvscan" and "dmsetup status"

Running 'fdisk -l' should give you an overview of attached storage, partitions and file system types.
Running 'pvscan' should show the Physical Volums (PV).
Running 'vgscan' the Volume Groups (VG).
Running 'vgchange -ay' should then enable your LVM.
Running 'lvscan; dmsetup status' afterwards should show the Logical Volumes (LV) and what directory they're attached to in /dev/ for mounting purposes. Now with 'mount /dev/VOLUMEGROUPNAME/LOGICALVOLUMENAME /some/directory' you can mount the LV, e.g.: 'mount /dev/vg0001/lv001 /mnt/temp/ -o ro' should mount LV name "lv001" inside the "vg0001" VG at mountpoint /mnt/temp read-only (as you wouldn't want to change things while making backups).