菜鸟学Linux 第023篇笔记 磁盘管理

菜鸟学Linux 第023篇笔记 磁盘管理

ln (make links between files)
ln [-s -v] SRC DEST

硬链接：
1、只能对文件创建，不能应用于目录；
2、不能跨文件系统；
3、创建硬链接会增加文件被链接的次数；

符号链接：
1、可应用于目录；
2、可以跨文件系统；
3、不会增加链接文件的链接次数；
4、其大小为指定的路径所包含的字符个数；

du (estimate file space usage)
-s (display only a total for each argument)
-h (print sizes in human readable format (e.g., 1K 234M 2G))
df (report file system disk space usage)

设备文件
b 按块为单位，随机访问的设备；硬盘
c 按字符为单位，线性设备；键盘

/dev
主设备号(major number)
标识设备类型
次设备号(minor number)
标识同一类型中不同设备
mknod (make block or character special files)
mknod [OPTION]... NAME TYPE [MAJOR MINOR]
-m set permission mode (as in chmod), not a=rw - umask

硬盘设备的设备文件名：
IDE,ATA hd
STAT sd
SCSI sd
USB sd
a,b,c...来区别同一种类型下的不同设备

IDE
第一个IDE口：主、从
/dev/hda, /dev/hdb
第二个IDE口：主、从
/dev/hdc, /dev/hdd

STAT, SCSI, USB
sda, sdb, sdc...

hda:
hda1 第一个主分区
hda2
hda3
hda4
hda5 第一个逻辑分区

查看当前系统几块硬盘命令
fdisk -l [/dev/..]

管理磁盘分区命令
fdisk /dev/sda
a toggle a bootable flag
b edit bsd disklabel
c toggle the dos compatibility flag
d delete a partition
l list known partition types
m print this menu
n add a new partition
o create a new empty DOS partition table
p print the partition table
q quit without saving changes
s create a new empty Sun disklabel
t change a partition's system id
u change display/entry units
v verify the partition table
w write table to disk and exit
x extra functionality (experts only)
(输入字符错误时，如要删除需同时按住Ctrl再按删除即可)
依照相应命令即可管理硬盘分区

查看当前系统的文件系统
cat /proc/partitions
通知系统重读分区表
partprobe
Description
partprobe is a program that informs the operating system kernel of par-
tition table changes, by requesting that the operating system re-read
the partition table.

cat /proc/filesystems
查看当前系统所支持的文件系统

VFS (Virtual FileSystem)
ext3, ext4, ext2, extended
reiserfs(suse)
iso9660, swap, cifs, nfs,
xfs, jfs
ocfs2, gfs2
fat32, ntfs...

Disk
Boot Block
Block Group 0
Super Block, GDT, block bitmap, inode bitmap, inode table, data blocks
Block Group 1
Block Group ...

block size: 1027, 2048, 4096
block group
inode: index node
super block
date structure: bitmap
Group description(GDT)

ext3, ext2区别
3 have journal file system

创建文件系统
mkfs (build a Linux file system)
mkfs.ext3
mkfs.ext2
mkfs.vfat format fat32
mke2fs (create an ext2/ext3 filesystem)
-j = mkfs.ext3
-b block-size
Specify the size of blocks in bytes. Valid block size vales are
1024, 2048 and 4096 bytes per block.
-L new-volume-label
Set the volume label for the filesystem to new-volume-
The maximum length of the volume label is 16 bytes.
-m reserved-blocks-percentage
Specify the percentage of the filesystem blocks reserved for the
super-user. This avoids fragmentation, and allows root-owned
daemons, such as syslogd(8), to continue to function correctly
after non-privileged processes are prevented from writing to the
filesystem. The default percentage is 5%.
e.g. mke2fs -m 5 /dev/sda1
-N number-of-inodes
overrides the default calculation of the number of inodes that
should be reserved for the filesystem (which is based on the
number of blocks and the bytes-per-inode ratio). This allows
the user to specify the number of desired inodes directly.
e.g. mke2fs -i 20480 /dev/sdb1
mke2fs -N 3028 /dev/sdb1
-F Force mke2fs to run, even if the specified device is not a block
special device, or appears to be mounted.

blkid (command-line utility to locate/print block device attributes)
UUID
TYPE
LABLE

e2lable 设备卷标
e2lable 设备文件 卷标(不加则显示设备卷标)

tune2fs (adjust tunable filesystem parameters on ext2/ext3 filesystems)
注意是无损文件！
-j: 不损害原有数据，将ext2升级为ext3;
-L: 设定或修改卷标
-m: Set the percentage of reserved filesystem blocks.
-o: [^]mount-option[,...] 设定默认挂载选项
-r reserved-blocks-count
Set the number of reserved filesystem blocks.
-l List the contents of the filesystem superblock.

dumpe2fs dump ext2/ext3 filesystem information
-h only display the superblock information and not any of the block
group descriptor detail information.

fsck (check and repair a Linux file system)
-t fslist
Specifies the type(s) of file system to be checked.

e2fsck (check a Linux ext2/ext3 file system)(专用于修复ext2,ext3文件系统)
-f Force checking even if the file system seems clean.
-p Automatically repair ("preen") the file system.

mkfs -t TYPE /dev/sdb# #为数字

mount挂载 /etc/fstab /etc/mtab
mount 显示当前系统已经挂载的设备及挂载点
-a Mount all filesystems (of the given types) mentioned in /etc/fstab.
-n Mount without writing in /etc/mtab. This is necessary for exam-
ple when /etc is on a read-only file system.
-t vfstype
The argument following the -t is used to indicate the file sys-
tem type.
-r Mount the file system read-only. A synonym is -o ro.
-w Mount the file system read/write. This is the default. A synonym
is -o rw.

mount device 挂载点
device:
设备文件: /dev/sdb*
卷标 LABLE=""
UUID UUID=""
挂载点
要求
1.此目录没有其它进程使用；
2.目录必须事先存在；
3.如目录中有文件，则文件会暂时隐藏；

umount 设备|挂载点
注意事项
挂载的设备没有进程使用

fuser (fuser - identify processes using files or sockets)
当umount时如果有人在使用该设备时，可使用该命令来查看谁在使用
-v Verbose mode.
Processes are shown in a ps-like style. The fields
-k Kill processes accessing the file. Unless changed
with -signal, SIGKILL is sent. An fuser process never
kills itself, but may kill other fuser processes. The
effective user ID of the process executing fuser is
set to its real user ID before attempting to kill.
-m name specifies a file on a mounted file system or a
block device that is mounted. All processes accessing
files on that file system are listed. If a directory
file is specified, it is automatically changed to
name/. to use any file system that might be mounted
on that directory.
e.g. fuser -vm /dev/sda1

开机自动挂载
os在启动时，会自动挂载下述文件中定义的每个文件系统
文件系统配置文件/etc/fstab
字段含义：
1. 设备(要挂载的设备) LABEL, UUID, 设备文件
2. 挂载点
3. 文件系统类型
4. 挂载选项(默认defaults)
5. 转储频率　数字表示多少天备份，０不备份
6. 开机自检次序(一般次序根为１)０表示不检查

THE LOOP DEVICE
One further possible type is a mount via the loop device. For example,
the command

mount /tmp/fdimage /mnt -t msdos -o loop=/dev/loop3,blocksize=1024

will set up the loop device /dev/loop3 to correspond to the file
/tmp/fdimage, and then mount this device on /mnt.

e.g.
挂载iso镜像，用来查看iso镜像内容
mount -o loop /path/name.iso /media/

swap partition分区
允许内存过载使用(不推荐)
当系统内存满载，如有新进程又需要内存，则内核会将当前物理内存中不被访问的
页框移至swap分区中，以保证新进程有内存空间可被使用；

command:
free (Display amount of free and used memory in the system)
-m Mb

mkswap (mkswap - set up a Linux swap area)(切记先设置分区类型为swap)
mkswap /dev/sda#
-L

swapon swapoff
e.g. swapon /dev/sdb6
swapon, swapoff - enable/disable devices and files for paging and swap-
ping
Swapon is used to specify devices on which paging and swapping are to
take place.

创建虚拟硬盘
dd (dd - convert and copy a file)
if=FILE
read from FILE instead of stdin
of=FILE
write to FILE instead of stdout
bs=BYTES
force ibs=BYTES and obs=BYTES
count=BLOCKS
copy only BLOCKS input blocks
seek=BLOCKS
skip BLOCKS obs-sized blocks at start of output

e.g.
backup MBR dd if=/dev/sdb of=/mnt/usb/mbr.backup bs=512 count=1
restore MBR dd if=/usb/mbr.backup of=/dev/sdb bs=512 count=1
CDROM > iso cat /dev/cdrom > /root/name.iso
临时救急创建交换分区
1.创建虚拟块文件 dd if=/dev/zero of=/var/swapfile bs=1M count=1024
2.格式化为swap分区 mkswap /var/swapfile
3.挂载swap swapon /var/swapfile