隨機數、熵池、mknod建立設備、fdisk磁盤管理、partprobe內核識別分區表

時間 2019-12-05

標籤隨機數 mknod 建立設備 fdisk 磁盤管理 partprobe 內核識別分區简体版

原文原文鏈接

隨機數、熵池

bash能夠生成隨機數，範圍是0-32768【65535/2】，它是一個系統變量$RANDOMlinux

[jiakang@jiakang tmp]$ echo $RANDOM
15163
[jiakang@jiakang tmp]$ echo $RANDOM
23259
[jiakang@jiakang tmp]$ echo $RANDOM
25631

隨機數生成器：熵池

熵池是存放隨機數的池子，咱們上面bash生成的隨機數安全性很低，甚至是經過算法能夠破解，因此出現了熵池；

熵池是讓/dev/random使用的，它產生的隨機數是硬件不規律造成的，好比咱們間隔按鼠標的時間，安全性很是高，熵池中的值是剪切過來的，因此可能會被用完出現阻塞用戶的進程。

/dev/urandom:也是取熵池中的隨機數，可是取完後會用bash自動模擬，不會出現阻塞。算法

/dev/random

/dev/urandom安全

mknod建立設備

mknod mydev c 66 0【c表明字符設備,ls - l每行的最前面那個字符表明文件類型,66表明主設備號，0表明次設備號】bash

[root@jiakang a]# mknod mydev c 66 0
[root@jiakang a]# ls -il            
總用量 28
412296 drwxr-xr-x. 3 root root  4096 3月  28 16:34 b
412310 -rwxr-xr-x. 1 root root   133 4月  13 14:34 case.sh
412301 crw-r--r--. 1 root root 66, 0 4月  15 18:42 mydev

還能夠在建立設備的時候指定使用權限dom

[root@jiakang a]# mknod -m 640 mydev1 c 66 1
[root@jiakang a]# ls -l
總用量 28
drwxr-xr-x. 3 root root  4096 3月  28 16:34 b
-rwxr-xr-x. 1 root root   133 4月  13 14:34 case.sh
crw-r--r--. 1 root root 66, 0 4月  15 18:42 mydev
crw-r-----. 1 root root 66, 1 4月  15 18:47 mydev1

當咱們有個硬件鏈接到linux上面，這個設備會有個本身的設備號，而後咱們的linux也有這個設備號，因此就對接上了。linux向這個設備號發送東西，就會發送到對應的硬件上。ide

下面是兩個設備【終端設備】：
ui

[root@jiakang a]# tty
/dev/pts/0

[jiakang@jiakang ~]$ tty
/dev/pts/1

[root@jiakang a]# echo "hello jiakang" >> /dev/pts/1

[jiakang@jiakang ~]$ hello jiakang

根目錄的重要性

根目錄是文件系統的訪問路口，如：/a/b，如今把b單獨分區了，我要想訪問b分區，必須先找到根目錄的/a/b，b文件存的是b分區的訪問入口；在/a/b/c中，如今再把c單獨分區，那訪問的時候先找根分區而後找到b文件相應的找到了b分區，再找c文件找到c分區。因此若是根很重要，根分區崩了，其餘分區也沒了this

fdisk查看/建立分區

查看

查看磁盤、分區的使用狀況 fdisk -l [/dev/PATH]操作系統

[root@jiakang ~]# fdisk -l盤【查看磁盤的使用狀況】

Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000478b0

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          26      204800   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              26         287     2097152   82  Linux swap / Solaris
Partition 2 does not end on cylinder boundary.
/dev/sda3             287        1306     8182784   83  Linux
[root@jiakang ~]# fdisk -l /dev/sda1【查看某個分區的使用狀況】

Disk /dev/sda1: 209 MB, 209715200 bytes
255 heads, 63 sectors/track, 25 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

建立、建立

fdisk /dev/sdacode

p：顯示當前硬件的分區，包括沒保存的改動
n：建立新分區【e：擴展分區 p：主分區】
d：刪除一個分區
w：保存退出
q：不保存退出
t：修改分區類型【L：顯示支持的分區類型】
l：顯示所支持的全部類型

下面的代碼我要建立一個新的主分區，可是沒有多餘的柱面【空間】了

[root@jiakang ~]# fdisk /dev/sda【管理磁盤分區】

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help): m【m獲取幫助】
Command action
   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)

Command (m for help): p【打印顯示當前分區使用情況】

Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders【共1305個柱面】
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000478b0

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          26      204800   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              26         287     2097152   82  Linux swap / Solaris
Partition 2 does not end on cylinder boundary.
/dev/sda3             287        1306     8182784   83  Linux

Command (m for help): n【建立新分區】
Command action
   e   extended
   p   primary partition (1-4)
p【建立主分區】
Selected partition 4
No free sectors available

Command (m for help): q【退出】
...

刪除第3個主分區，而後再從新劃分柱面

...
...
Command (m for help): d【刪除分區】
Partition number (1-4): 3【刪除第三個主分區】

Command (m for help): p

Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000478b0

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          26      204800   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              26         287     2097152   82  Linux swap / Solaris
Partition 2 does not end on cylinder boundary.

建立主分區3，擴展分區4，邏輯分區5

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 3
First cylinder (287-1305, default 287): 【起始柱面，這直接回車就是默認】
Using default value 287
Last cylinder, +cylinders or +size{K,M,G} (287-1305, default 1305): +2G【結束柱面，指定大小】

Command (m for help): p

Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000478b0

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          26      204800   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              26         287     2097152   82  Linux swap / Solaris
Partition 2 does not end on cylinder boundary.
/dev/sda3             287         548     2098834   83  Linux【這是新增的主分區3柱面287-548】

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
e【建立擴展分區】
Selected partition 4
First cylinder (549-1305, default 549): 【回車】
Using default value 549
Last cylinder, +cylinders or +size{K,M,G} (549-1305, default 1305): 【回車】
Using default value 1305

Command (m for help): n
First cylinder (549-1305, default 549): 
Using default value 549
Last cylinder, +cylinders or +size{K,M,G} (549-1305, default 1305): +1G

Command (m for help): p

Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000478b0

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          26      204800   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              26         287     2097152   82  Linux swap / Solaris
Partition 2 does not end on cylinder boundary.
/dev/sda3             287         548     2098834   83  Linux
/dev/sda4             549        1305     6080602+   5  Extended
/dev/sda5             549         680     1060258+  83  Linux【類型編號83，類型Linux】

上面的sda5類型編號是83，類型爲Linux，咱們能夠調到其餘類型

Command (m for help): t【修改分區類型】
Partition number (1-5): 5【修改第5個分區】
Hex code (type L to list codes): L【查看有哪些分區類型，83就是剛纔的Linux】

 0  Empty           24  NEC DOS         81  Minix / old Lin bf  Solaris        
 1  FAT12           39  Plan 9          82  Linux swap / So c1  DRDOS/sec (FAT-
 2  XENIX root      3c  PartitionMagic  83  Linux           c4  DRDOS/sec (FAT-
 3  XENIX usr       40  Venix 80286     84  OS/2 hidden C:  c6  DRDOS/sec (FAT-
 4  FAT16 <32M      41  PPC PReP Boot   85  Linux extended  c7  Syrinx         
 5  Extended        42  SFS             86  NTFS volume set da 
...
...
Hex code (type L to list codes): 82【調整爲82交換分區】
Changed system type of partition 5 to 82 (Linux swap / Solaris)

Command (m for help): p

Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000478b0

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          26      204800   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              26         287     2097152   82  Linux swap / Solaris
Partition 2 does not end on cylinder boundary.
/dev/sda3             287         548     2098834   83  Linux
/dev/sda4             549        1305     6080602+   5  Extended
/dev/sda5             549         680     1060258+  82  Linux swap / Solaris【改成了82】

w 保存退出修改

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: 設備或資源忙.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.
[root@jiakang ~]# fdisk -l

Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000478b0

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          26      204800   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              26         287     2097152   82  Linux swap / Solaris
Partition 2 does not end on cylinder boundary.
/dev/sda3             287         548     2098834   83  Linux
/dev/sda4             549        1305     6080602+   5  Extended
/dev/sda5             549         680     1060258+  82  Linux swap / Solaris

partprobe讓內核從新識別分區表

上面的分區表成功後須要內核去識別，/proc/partitions目錄是當前內核識別的分區表，能夠經過partprobe去讓內核從新識別，可是在這可能遇到下面的錯誤

[root@jiakang ~]# cat /proc/partitions
major minor  #blocks  name

   8        0   10485760 sda
   8        1     204800 sda1
   8        2    2097152 sda2
   8        3    8182784 sda3
[root@jiakang ~]# partprobe
Warning: WARNING: the kernel failed to re-read the partition table on /dev/sda (設備或資源忙).  As a result, it may not reflect all of your changes until after reboot.
Warning: 沒法以讀寫方式打開 /dev/sr0 (只讀文件系統)。/dev/sr0 已按照只讀方式打開。
Warning: 沒法以讀寫方式打開 /dev/sr0 (只讀文件系統)。/dev/sr0 已按照只讀方式打開。
Error: 無效的分區表 - /dev/sr0 出現遞歸分區。
[root@jiakang ~]# cat /proc/partitions
major minor  #blocks  name

   8        0   10485760 sda
   8        1     204800 sda1
   8        2    2097152 sda2
   8        3    8182784 sda3
[root@jiakang ~]# ls -l /dev/sr0
brw-rw----+ 1 root cdrom 11, 0 4月  16 09:55 /dev/sr0

從上面的結果看，sr0是光驅設備，百度了下/dev/sr0這個設備，也所是光驅。因而管它重載分區表失敗是否是因爲「Error: 無效的分區表 - /dev/sr0 出現遞歸分區。」引發的，先把光驅移除了再說，反正是虛擬機上。

把虛擬機上的光驅設備移除後，從新啓動系統，再從新新建分區，並從新執行partprobe命令重載分區表，錯誤信息「Error: 無效的分區表 - /dev/sr0 出現遞歸分區。」沒有了，只是警告提示「設備或資源忙」還在。這時直接格式化新建的邏輯分區/dev/sda5仍是提示「沒有那個文件或目錄」。因而重啓系統，再格式化/dev/sda5，這回成功了。

也就是說，以前新建分區格式化失敗，是因爲虛擬機的光驅/dev/sr0設備致使了分區表遞歸。另外因爲是在同一塊硬盤上操做，因此必需要重啓系統才能使新建的分區寫入分區表生效。

卸載光驅後：

[root@jiakang ~]# partprobe           
Warning: WARNING: the kernel failed to re-read the partition table on /dev/sda (設備或資源忙).  As a result, it may not reflect all of your changes until after reboot.
[root@jiakang ~]# cat /proc/partitions
major minor  #blocks  name

   8        0   10485760 sda
   8        1     204800 sda1
   8        2    2097152 sda2
   8        3    8182784 sda3

重啓系統

MDZZ！！！不知道有沒有發現上面的剛開始柱面不足,我刪除了第3個主分區，個人根目錄及全部的文件都在裏面，至關於刪除了根目錄，致使系統崩潰：「客戶機操做系統已禁用 CPU。請關閉或重置虛擬機」

從新安裝了一下linux，此次我加載了兩塊磁盤，新建了sdb1分區：

[root@localhost ~]# fdisk -l

Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0002b305

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          26      204800   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              26         548     4194304   83  Linux
Partition 2 does not end on cylinder boundary.
/dev/sda3             548         809     2097152   82  Linux swap / Solaris
Partition 3 does not end on cylinder boundary.
/dev/sda4             809        1306     3988480    5  Extended
/dev/sda5             810        1306     3987456   83  Linux

Disk /dev/sdb: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xd25c91c2

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1         200     1606468+  83  Linux

然而此次發現不用內核去識別了，直接就能夠自動去識別，並且還能夠格式化【我sdb1是新建的剛剛】

[root@localhost ~]# cat /proc/partitions
major minor  #blocks  name

   8        0   10485760 sda
   8        1     204800 sda1
   8        2    4194304 sda2
   8        3    2097152 sda3
   8        4          1 sda4
   8        5    3987456 sda5
   8       16   10485760 sdb
   8       17    1606468 sdb1
[root@localhost ~]# mkfs -t ext4 /dev/sdb1
mke2fs 1.41.12 (17-May-2010)
文件系統標籤=
操做系統:Linux
...
...

查閱資料獲取的信息是：不是當前使用的磁盤不須要讓內核從新去獲取了，教訓就是沒事就快照，別不當心刪了根目錄！！

partx

redhat6的partprobe失效能夠用partx

[root@localhost ~]# partx -a /dev/sdb1 /dev/sdb

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