The DD command in Linux

The DD command copies a file with a block of the specified size and makes the specified conversion at the same time as the copy.

How to use: DD [OPERAND]

Parameter comment:

  bs=BYTES        read and write BYTES  bytes at a time  (also see ibs=,obs=)   cbs=BYTES        convert BYTES bytes at a time  conv=CONVS       convert the file as per the comma separated  symbol list  count=n         copy only  n input blocks  ibs=bytes       read bytes  bytes at a time  (default: 512)   if=FILE          read from file instead of stdin (default is standard input)   iflag= flags     read as per the comma separated symbol  List  obs=bytes       write bytes bytes at a time  (Default:  512)   of=file         write to file  instead of stdout (default to standard output)   oflag=flags     write as  per the comma separated symbol list  seek=BLOCKS      skip blocks obs-sized blocks at start of output  skip =blocks     skip blocks ibs-sized blocks at start of  input  status=WHICH    WHICH info to suppress  outputting to stderr;                    ' Noxfer '  suppresses transfer stats,  ' None '  suppresses  all

Optional parameters for Convs

  ascii     from EBCDIC to ASCII  ebcdic     from ASCII to EBCDIC  ibm        from ascii to alternate ebcdic  block     pad  newline-terminated records with spaces to cbs-size  unblock    replace trailing spaces in cbs-size records with newline   Lcase     change upper case to lower case  nocreat    do not create the output file  excl       fail if the output file already exists  notrunc    do not truncate the output file  ucase      change lower&nbsP;case to upper case  sparse    try to seek rather  than write the output for NUL input blocks  swab       swap every pair of input bytes  noerror    continue after read errors  sync      pad  every input block with NULs to ibs-size; when used             with block or unblock, pad  with spaces rather than nuls  fdatasync  physically write  output file data before finishing  fsync      Likewise, but also write metadata

Optional parameters for flags

  append    append mode  (makes sense only for  output; conv=notrunc suggested)   direct    use direct i/o  for data  directory  fail unless a directory  dsync      use synchronized I/O for data  sync       likewise, but also for metadata  fullblock   accumulate full blocks of input  (iflag only)   nonblock  use  non-blocking i/o  noatime   do not update access time   noctty    do not assign controlling terminal from  file  nofollow  do not follow symlinks  count_bytes   treat  ' Count=n '  as a byte count  (iflag only) 

Note: Where the number is specified, it is multiplied by the corresponding number if it ends with the following characters:

C =1, W =2, b =512, KB =1000, K =1024, MB =1000*1000, M =1024*1024, XM =m

GB =1000*1000*1000, G =1024*1024*1024, and so on for T, P, E, Z, Y

Ii. Examples of Use

1, the local/DEV/HDB full disk backup to/DEV/HDD

DD If=/dev/hdb OF=/DEV/HDD

2. Back up/DEV/HDB full data to the image file of the specified path

DD If=/dev/hdb Of=/root/image

3, backup/DEV/HDB overall data, and use the Gzip tool to compress, save to the specified path

DD If=/dev/hdb | gzip >/root/image.gz

4. Split a file into 3 files

#文件大小为2.3k[[email protected] ~]$ ll db1_db_links.sql -rw-r--r-- 1 oracle  oinstall 2344 nov 21 10:39 db1_db_links.sql# this file into every file 1k,bs=1k,count= 1, use the skip parameter to specify how many BS support reads are skipped in the input file [[Email protected] ~]$ dd if=db1_db_links.sql of=dd01.sql  bs=1k count=11+0 records in1+0 records out1024 bytes  (1.0 KB)  copied, 4.5536e-05 s, 22.5 mb/s[[email protected] ~]$ dd if=db1_ Db_links.sql of=dd02.sql bs=1k count=1 skip=11+0 records in1+0 records  out1024 bytes  (1.0 KB)  copied, 0.000146387 s, 7.0 mb/s[[email  protected] ~]$ dd if=db1_db_links.sql of=dd03.sql bs=1k count=1 skip= 20+1 records in0+1 records out296 bytes  (296 b)  copied,  0.000204216 s, 1.4 mb/s# SplitThe file [[email protected] ~]$ ll dd*sql-rw-r--r-- 1 oracle oinstall 1024  May 20 14:58 dd01.sql-rw-r--r-- 1 oracle oinstall 1024 May  20 14:58 dd02.sql-rw-r--r-- 1 oracle oinstall  296 may 20  14:58 dd03.sql

5. Merge the split files into 1

#合并操作, the Seek parameter is used to specify the number of BS skipped in the input file [[email protected] ~]$ dd of=1.sql if=dd01.sql 2+0 records in2+0 records out1024 bytes (1 .0 KB) copied, 0.000176 s, 5.8 mb/s[[email protected] ~]$ dd of=1.sql if=dd02.sql bs=1k seek=11+0 Records in1+0 Records OU  t1024 bytes (1.0 kB) copied, 0.000124038 s, 8.3 mb/s[[email protected] ~]$ dd of=1.sql if=dd03.sql bs=1k seek=20+1 Records In0+1 Records out296 bytes (296 B) copied, 0.00203881 S, 145 kb/s# and pre-split file verification [[Email protected] ~]$ diff 1.sql Db1_db_lin Ks.sql[[email protected] ~]$

6. Inserting data in the location specified in the output file without truncating the output file

Need to use conv=notrunc parameter [[email protected] ~]$ dd if=2.sql of=1.sql bs=1k seek=1 count=2 conv=notrunc

Reference: http://blog.csdn.net/xizaihui/article/details/53307578

http://blog.csdn.net/jijiagang/article/details/42192049

This article is from the "DBA fighting!" blog, so be sure to keep this source http://hbxztc.blog.51cto.com/1587495/1927774

The DD command in Linux