我执行了以下程序,以便为交换添加400米,
我从sdb磁盘中取出400米以进行交换增加
一切都很好,但在最后一个命令之前,我表演了
mkswap /dev/rootvg/swap
我从mkswap收到以下警告消息
mkswap: /dev/rootvg/swap: warning: don't erase bootbits sectors
on whole disk. Use -f to force.
Setting up swapspace version 1,size = 2490364 KiB
no label,UUID=2f42fa37-987d-40a5-8cf6-5707e1d8f077
最后交换按预期扩展到2.4G
但是我很担心来自mkswap命令的警告消息
请告知警告的含义：
mkswap: /dev/rootvg/swap: warning: don't erase bootbits sectors on whole disk. Use -f to force.
如果这样可以吗？
我在linux redhat机器上的程序 – 版本6
# swapon -s
Filename Type Size Used Priority
/dev/dm-1 partition 2064380 0 -1
# free
total used free shared buffers cached
Mem: 5991892 539036 5452856 212 70444 270664
-/+ buffers/cache: 197928 5793964
Swap: 2064380 0 2064380
# pvs
PV VG Fmt Attr PSize PFree
/dev/sdb rootvg lvm2 a--u 7.97g 416.00m
/dev/sdc orahome lvm2 a--u 30.00g 15.00g
# lsblk /dev/sdb
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sdb 8:16 0 8G 0 disk
|-rootvg-swap (dm-1) 253:1 0 2G 0 lvm [SWAP]
|-rootvg-slash (dm-2) 253:2 0 576M 0 lvm /
|-rootvg-usr (dm-3) 253:3 0 1.4G 0 lvm /usr
|-rootvg-home (dm-4) 253:4 0 256M 0 lvm /home
|-rootvg-opt (dm-5) 253:5 0 416M 0 lvm /opt
`-rootvg-var (dm-6) 253:6 0 3G 0 lvm /var
# swapon -s
Filename Type Size Used Priority
/dev/dm-1 partition 2064380 0 -1
# swapoff /dev/rootvg/swap
# lvresize /dev/rootvg/swap -L +400m
Rounding size to boundary between physical extents: 416.00 MiB.
Size of logical volume rootvg/swap changed from 1.97 GiB (63 extents) to 2.38 GiB (76 extents).
Logical volume swap successfully resized.
# mkswap /dev/rootvg/swap
mkswap: /dev/rootvg/swap: warning: don't erase bootbits sectors
on whole disk. Use -f to force.
Setting up swapspace version 1,UUID=2f42fa37-987d-40a5-8cf6-5707e1d8f077
# swapon /dev/rootvg/swap
# free
total used free shared buffers cached
Mem: 5991892 539680 5452212 212 70536 270892
-/+ buffers/cache: 198252 5793640
Swap: 2490364 0 2490364
解决方法
看起来像一个安全预防措施,以防止您破坏引导扇区等…当您可能打算使用分区时使用整个磁盘.
此警告消息不再出现在CentOS 6.5和Ubuntu 16.04中.
这个较旧的(2006)mkswap.c模糊地定义了bootbits：http://code.metager.de/source/xref/busybox/util-linux/mkswap.c
/* char bootbits[1024]; Space for disklabel etc. */
从CentOS 6.5 mkswap.c：
if (is_whole_disk_fd(fd,devname)) {
/* don't zap bootbits on whole disk -- we know nothing
* about bootloaders on the device */
whole = 1;
zap = 0;
我对C并不陌生,但新代码看起来更智能,可能保留了引导数据.我不是那么深思.
