Swap不足怎么办
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1. 使用dd命令新建一个文件并挂载为SWAP
Use command 'dd' to create a file and mount as swap
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[root@localhost ~]# free -m
total used free shared buffers cached
Mem: 5966 334 5631 0 16 99
-/+ buffers/cache: 218 5747
Swap: 6143 0 6143
[root@localhost ~]# dd if=/dev/zero of=/root/swap bs=1024 count=1024000
1024000+0 records in
1024000+0 records out
1048576000 bytes (1.0 GB) copied, 3.20295 s, 327 MB/s
bs=是bytes,count是 blocks 个块，1024bytes=1K，1024000K=1000M
[root@localhost ~]# mkswap /root/swap
mkswap: /root/swap: warning: don't erase bootbits sectors
on whole disk. Use -f to force.
Setting up swapspace version 1, size = 1023996 KiB
no label, UUID=af12e46f-16da-4b89-a89f-301bdce4b138
[root@localhost ~]# swapon /root/swap
[root@localhost ~]# free -m
total used free shared buffers cached
Mem: 5966 1604 4361 0 21 1217
-/+ buffers/cache: 365 5600
Swap: 7143 0 7143
与最开始的相比，增加了近1000M
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2. 用 fdisk 将未使用的分区格式化，并挂载为swap分区
use 'fdisk' to format other partitions and mount as swap
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[root@localhost ~]# fdisk -l
Disk /dev/sda: 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
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 2078 16587112+ 83 Linux
/dev/sda3 2079 2600 4192965 82 Linux swap / Solaris
[root@localhost ~]# fdisk /dev/sda
The number of cylinders for this disk is set to 2610.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
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
Disk /dev/sda: 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
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 2078 16587112+ 83 Linux
/dev/sda3 2079 2600 4192965 82 Linux swap / Solaris
Command (m for help): n
Command action
e extended
p primary partition (1-4)
e
Selected partition 4
First cylinder (2601-2610, default 2601):
Using default value 2601
Last cylinder or +size or +sizeM or +sizeK (2601-2610, default 2610): +50M ---新增加个50M的扩展分区。
---add a extend partition of 50M
Command (m for help): p
Disk /dev/sda: 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
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 2078 16587112+ 83 Linux
/dev/sda3 2079 2600 4192965 82 Linux swap / Solaris
/dev/sda4 2601 2607 56227+ 5 Extended
Command (m for help): n
First cylinder (2601-2607, default 2601):
Using default value 2601
Last cylinder or +size or +sizeM or +sizeK (2601-2607, default 2607):
Using default value 2607
Command (m for help): p
Disk /dev/sda: 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
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 2078 16587112+ 83 Linux
/dev/sda3 2079 2600 4192965 82 Linux swap / Solaris
/dev/sda4 2601 2607 56227+ 5 Extended
/dev/sda5 2601 2607 56196 83 Linux
Command (m for help): w
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@bys3 ~]# free -m
total used free shared buffers cached
Mem: 2013 218 1795 0 15 153
-/+ buffers/cache: 49 1964
Swap: 5094 0 5094
[root@bys3 ~]# swapoff /root/swap 关闭一个SWAP空间
off a swap space
[root@bys3 ~]# free -m
total used free shared buffers cached
Mem: 2013 218 1795 0 15 153
-/+ buffers/cache: 49 1964
Swap: 4094 0 4094
[root@bys3 ~]# mkswap /dev/sda5
/dev/sda5: No such file or directory
[root@bys3 ~]# partprobe ---同步分区表
sync of partition table
Warning: Unable to open /dev/sr0 read-write (Read-only file system). /dev/sr0 has been opened read-only.
Segmentation fault
[root@bys3 ~]# mkswap /dev/sda5
Setting up swapspace version 1, size = 57540 kB
[root@bys3 ~]# swapon /dev/sda5
[root@bys3 ~]# free -m
total used free shared buffers cached
Mem: 2013 218 1795 0 15 153
-/+ buffers/cache: 49 1964
Swap: 4149 0 4149
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开机自动挂载
auto mount during boot process
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[root@localhost ~]# vi /etc/fstab
LABEL=/ / ext3 defaults 1 1
LABEL=/boot /boot ext3 defaults 1 2
tmpfs /dev/shm tmpfs defaults 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
sysfs /sys sysfs defaults 0 0
proc /proc proc defaults 0 0
LABEL=SWAP-sda3 swap swap defaults 0 0
/root/swap swap swap defaults -------dd 挂载方式（dd mount）
/dev/sda5 swap swap defaults 0 0 -------格式化挂载方式（formatting partition mount）
[root@localhost ~]# mount -a ---------无报错则挂载成功（No errors then mount succeed）
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