Application of Linux dd command in SWAP partition Expansion

Application of Linux dd command in SWAP partition Expansion

I. basic functions of swap partitions in Linux:

Linux swap partitions are Linux swap partitions: When the Linux system has insufficient physical memory, the system automatically enables swap partitions to relieve the pressure on the physical memory, the system moves memory objects with low access frequency in the physical memory to the swap partition, and then generates a new connection in the physical memory to point to a specific object in the swap partition;

II,
Compared with busy servers, physical memory and physical partitions are insufficient at the same time. At this time, we need to temporarily expand the size of swap partitions. There are two ways to achieve this:

1. When the extended partitions of the hard disk still have available memory, you can use the fdisk command to create a new partition, adjust the partition type to Linux-swap, and then enable it.

Procedure:

[Root @ bkjia ~] # Free-m // view the usage of physical memory and swap partitions
Total used free shared buffers cached
Mem: 502 474 28 0 76 274
-/+ Buffers/cache: 124 378
Swap: 1019 0 1019
[Root @ bkjia ~] # Fdisk/dev/sdb

The number of cylinders for this disk is set to 2610.
There is nothing wrong with that, but this is larger than 1024,
And coshould in certain setups cause problems:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(E.g., dos fdisk, OS/2 FDISK)

Command (m for help): p // list the partitions currently created

Disk/dev/sdb: 21.4 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065*512 = 8225280 bytes

Device Boot Start End Blocks Id System

Command (m for help): n // create a partition
Command action
E extended
P primary partition (1-4)
P // primary Partition
Partition number (1-4): 1
First cylinder (1-2610, default 1 ):
Using default value 1
Last cylinder or + size or + sizeM or + sizeK (1-2610, default 2610): + 3G
Command (m for help): t // change the partition type

Selected partition 1
Hex code (type L to list codes): L // list partitions supported by the kernel

0 Empty 1e Hidden W95 FAT1 80 Old Minix bf Solaris
1 FAT12 24 nec dos 81 Minix/old Lin c1 DRDOS/sec (FAT-
2 XENIX root 39 Plan 9 82 Linux swap/So c4 DRDOS/sec (FAT-
3 XENIX usr 3c PartitionMagic 83 Linux c6 DRDOS/sec (FAT-
4 FAT16 <32 M 40 Venix 80286 84 OS/2 hidden C: c7 Syrinx
5 Extended 41 PPC PReP Boot 85 Linux extended da Non-FS data
6 FAT16 42 SFS 86 NTFS volume set db CP/M/CTOS /.
7 HPFS/NTFS 4d QNX4.x 87 NTFS volume set de Dell Utility
8 AIX 4e QNX4.x 2nd part 88 Linux plaintext df BootIt
9 AIX bootable 4f QNX4.x 3rd part 8e Linux LVM e1 DOS access
A OS/2 Boot Manag 50 OnTrack DM 93 Amoeba e3 DOS R/O
B W95 FAT32 51 OnTrack DM6 Aux 94 Amoeba BBT e4 SpeedStor
C W95 FAT32 (LBA) 52 CP/M 9f BSD/OS eb BeOS fs
E W95 FAT16 (LBA) 53 OnTrack DM6 Aux a0 IBM Thinkpad hi ee EFI GPT
F W95 Ext 'd (LBA) 54 OnTrackDM6 a5 FreeBSD ef EFI (FAT-12/16/
10 OPUS 55 EZ-Drive a6 OpenBSD f0 Linux/PA-RISC B
11 Hidden FAT12 56 Golden Bow a7 NeXTSTEP f1 SpeedStor
12 Compaq diagnost 5c Priam Edisk a8 Darwin UFS f4 SpeedStor
14 Hidden FAT16 <3 61 SpeedStor a9 NetBSD f2 DOS secondary
16 Hidden FAT16 63 gnu hurd or Sys AB Darwin boot fb VMware VMFS
17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs fc VMware VMKCORE
18 AST SmartSleep 65 Novell Netware b8 BSDI swap fd Linux raid auto
1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid fe LANstep
1c Hidden W95 FAT3 75 PC/IX be Solaris boot ff BBT
Hex code (type L to list codes): 82
Changed system type of partition 1 to 82 (Linux swap/Solaris)

Command (m for help): w // Save the partition
The partition table has been altered!

Calling ioctl () to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.

[Root @ bkjia ~] # Partprobe/dev/sdb // Let the kernel re-read the Partition Table
[Root @ bkjia ~] # Cat/proc/partitions // ensure that the kernel re-reads the partition table.
Major minor # blocks name

8, 0, 20971520, sda
8 1 305203 sda1
8 2 19615365 sda2
8, 3, 1044225, sda3
8 16 20971520 sdb
8 17 2939863 sdb1
[Root @ bkjia ~] # Mkswap/dev/sdb1 // format
Setting up swapspace version 1, size = 3010412 kB
[Root @ bkjia ~] # Swapon/dev/sdb1 // enable this swap Partition
[Root @ bkjia ~] # Free-m
Total used free shared buffers cached
Mem: 502 394 107 0 30 273
-/+ Buffers/cache: 90 412
Swap: 3890 0 3890

[Root @ bkjia ~] # Swapoff/dev/sdb1 // disable this swap Partition
[Root @ bkjia ~] # Free-m
Total used free shared buffers cached
Mem: 502 393 108 0 30 273
-/+ Buffers/cache: 89 413.
Swap: 1019 0 1019

2. When there is no remaining storage on the hard disk to create a new partition, you can use the dd command to create a file in the existing partition and act as the swap partition.
Specific steps: (the current script is displayed)
[Root @ bkjia ~] # Vi createswap. sh
#! /Bin/bash
Echo-n "Please input your number :"
Read number
Echo-n "Please input your swapfile name and the whole path :"
Read path
Dd if =/dev/zero of = $ path bs = 1 M count = $ number
Mkswap $ path
Swapon $ path
Free-m
Echo "The swap created"

Conclusion: This tutorial is complete.

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