I have a need to find all of the writable storage devices attached to a given machine, whether or not they are mounted.
The dopey way to do this would be to try every entry in /dev that corresponds to a writable devices (hd* and sd*)......
Is there a better solution, or should I stick with this one?
/proc/partitions will list all the block devices and partitions that the system recognizes. You can then try using file -s <device> to determine what kind of filesystem is present on the partition, if any.
You can always do fdisk -l which seems to work pretty well, even on strange setups such as EC2 xvda devices.
Here is a dump for a m1.large instance:
root@ip-10-126-247-82:~# fdisk -l
Disk /dev/xvda1: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders, total 20971520 sectors
Units = sectors of 1 * 512 = 512 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/xvda2: 365.0 GB, 365041287168 bytes
255 heads, 63 sectors/track, 44380 cylinders, total 712971264 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/xvda2 doesn't contain a valid partition table
Disk /dev/xvda3: 939 MB, 939524096 bytes
255 heads, 63 sectors/track, 114 cylinders, total 1835008 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/xvda3 doesn't contain a valid partition table
While mount says:
root@ip-10-126-247-82:~# mount
/dev/xvda1 on / type ext4 (rw)
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
fusectl on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
udev on /dev type devtmpfs (rw,mode=0755)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
tmpfs on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755)
none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880)
none on /run/shm type tmpfs (rw,nosuid,nodev)
/dev/xvda2 on /mnt type ext3 (rw)
And /proc/partitions says:
root@ip-10-126-247-82:~# cat /proc/partitions
major minor #blocks name
202 1 10485760 xvda1
202 2 356485632 xvda2
202 3 917504 xvda3
How fdisk -l works is something I would love to know myself.