Getting partition's size

Getting the size of a partition in Linux is very simple if you're logged in as root:

olimpo:~# fdisk -l /dev/sda

Disk /dev/sda: 160.0 GB, 160000000000 bytes
255 heads, 63 sectors/track, 19452 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: 0xabd592d5

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        1567    12586896    7  HPFS/NTFS
/dev/sda2            1568        2546     7863817+  17  Hidden HPFS/NTFS
/dev/sda3            2547        2796     2008125   82  Linux swap / Solaris
/dev/sda4            2797       19452   133789320   83  Linux

But it might be that you're just a DBA with access only to some partitions instead of the whole disk, and you got this server with no idea about partition sizes. If this is the case, then you can still know the size of your partitions with fdisk:

oracle@olimpo:/myASM$ /sbin/fdisk -l /dev/sda
Cannot open /dev/sda
oracle@olimpo:/myASM$ ls -la
total 8
drwxr-xr-x   2 oracle dba  4096 Oct 25 12:15 .
drwxr-xr-x 113 root   root 4096 Oct 25 12:15 ..
brw-rw----   1 oracle dba  8, 4 Oct  3 08:44 sda4
oracle@olimpo:/myASM$ /sbin/fdisk -s sda4
133789320

In Solaris is a bit different as the -s flag is not the same as in Linux:

oracle@myserver:/myASM$ ls -la
total 4
drwxr-xr-x   2 oracle   dba          512 Oct 22  2008 .
drwxr-xr-x  38 root     root        1024 Oct 18 16:57 ..
crw-r--r--   1 oracle   dba       32, 24 Oct 22  2008 disk1
crw-r--r--   1 oracle   dba       32, 25 Oct 25 09:31 disk2
crw-r--r--   1 oracle   dba       32, 26 Oct 22  2008 disk3

oracle@myserver:/myASM$ /sbin/fdisk -Rg disk2
* Label geometry for device disk2
* PCYL     NCYL     ACYL     BCYL     NHEAD NSECT SECSIZ
  35135    35135    2        0        64    255   512   

oracle@myserver:/myASM$ echo "(35135*64*255*512)/1024/1024"|bc
279982

With the last command you calculate the partition size in megabytes.