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Top Forums UNIX for Dummies Questions & Answers Help Understanding Output and question about /dev/ Post 302332575 by pludi on Thursday 9th of July 2009 01:17:57 PM
Old 07-09-2009
For future reference, please use [code][/code] tags for listings, source code, ...

Quote:
Originally Posted by mojoman
Code:
Disk /dev/sda: 17849 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0

   Device Boot Start     End   #cyls    #blocks   Id  System
/dev/sda1   *      0+    499     500-   4016218+  83  Linux
/dev/sda2        500     999     500    4016250   82  Linux swap / Solaris
/dev/sda3       1000   17848   16849  135339592+  83  Linux
/dev/sda4          0       -       0          0    0  Empty

This means that each of the 500 cylinders allocated for /dev/sda2 is 8225280 bytes (or about 8MB) large, which is about 4GB in total. Or, from the next column, it consists of 4016250 blocks á 1024 bytes = ~4GB.

You can specify the intended size by using '+1024M' (=1GB) when fdisk asks for the ending block number.

Quote:
Originally Posted by mojoman
One other question:
/dev/shm 517172 0 517172 0% /dev/shm

Is /dev/shm the swap partition /dev/sda2?
No, it's a pseudo filesystem (much like /dev, /proc, /sys) used for shared memory usage (IPC/Message passing). Swap partitions don't show up in the output of mount/df. Use swapon -s for that.
 

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PARTX(8)						       System Administration							  PARTX(8)

NAME
partx - tell the kernel about the presence and numbering of on-disk partitions SYNOPSIS
partx [-a|-d|-P|-r|-s|-u] [-t type] [-n M:N] [-] disk partx [-a|-d|-P|-r|-s|-u] [-t type] partition [disk] DESCRIPTION
Given a device or disk-image, partx tries to parse the partition table and list its contents. It can also tell the kernel to add or remove partitions from its bookkeeping. The disk argument is optional when a partition argument is provided. To force scanning a partition as if it were a whole disk (for example to list nested subpartitions), use the argument "-" (hyphen-minus). For example: partx --show - /dev/sda3 This will see sda3 as a whole-disk rather than as a partition. partx is not an fdisk program - adding and removing partitions does not change the disk, it just tells the kernel about the presence and numbering of on-disk partitions. OPTIONS
-a, --add Add the specified partitions, or read the disk and add all partitions. -b, --bytes Print the SIZE column in bytes rather than in human-readable format. -d, --delete Delete the specified partitions or all partitions. -g, --noheadings Do not print a header line with --show or --raw. -l, --list List the partitions. Note that all numbers are in 512-byte sectors. This output format is DEPRECATED in favour of --show. Do not use it in newly written scripts. -n, --nr M:N Specify the range of partitions. For backward compatibility also the format M-N is supported. The range may contain negative num- bers, for example --nr -1:-1 means the last partition, and --nr -2:-1 means the last two partitions. Supported range specifications are: M Specifies just one partition (e.g. --nr 3). M: Specifies the lower limit only (e.g. --nr 2:). :N Specifies the upper limit only (e.g. --nr :4). M:N Specifies the lower and upper limits (e.g. --nr 2:4). -o, --output list Define the output columns to use for --show, --pairs and --raw output. If no output arrangement is specified, then a default set is used. Use --help to get list of all supported columns. This option cannot be combined with the --add, --delete, --update or --list options. -P, --pairs List the partitions using the KEY="value" format. -r, --raw List the partitions using the raw output format. -s, --show List the partitions. The output columns can be selected and rearranged with the --output option. All numbers (except SIZE) are in 512-byte sectors. -t, --type type Specify the partition table type. --list-types List supported partition types and exit. -u, --update Update the specified partitions. -S, --sector-size size Overwrite default sector size. -v, --verbose Verbose mode. -V, --version Display version information and exit. -h, --help Display help text and exit. EXAMPLES
partx --show /dev/sdb3 partx --show --nr 3 /dev/sdb partx --show /dev/sdb3 /dev/sdb All three commands list partition 3 of /dev/sdb. partx --show - /dev/sdb3 Lists all subpartitions on /dev/sdb3 (the device is used as whole-disk). partx -o START -g --nr 5 /dev/sdb Prints the start sector of partition 5 on /dev/sdb without header. partx -o SECTORS,SIZE /dev/sda5 /dev/sda Lists the length in sectors and human-readable size of partition 5 on /dev/sda. partx --add --nr 3:5 /dev/sdd Adds all available partitions from 3 to 5 (inclusive) on /dev/sdd. partx -d --nr :-1 /dev/sdd Removes the last partition on /dev/sdd. SEE ALSO
addpart(8), delpart(8), fdisk(8), parted(8), partprobe(8) AUTHORS
Davidlohr Bueso <dave@gnu.org> Karel Zak <kzak@redhat.com> The original version was written by Andries E. Brouwer <aeb@cwi.nl>. ENVIRONMENT
LIBBLKID_DEBUG=all enables libblkid debug output. AVAILABILITY
The partx command is part of the util-linux package and is available from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils /util-linux/>. util-linux December 2014 PARTX(8)
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