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(默認為標準輸入) 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(默認為標準輸出) 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

 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 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

 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)

c =1, w =2, b =512, kB =1000, K =1024, MB =1000*1000, M =1024*1024, xM =MGB =1000*1000*1000, G =1024*1024*1024, and so on for T, P, E, Z, Y

dd if=/dev/hdb of=/dev/hdd

dd if=/dev/hdb of=/root/image

dd if=/dev/hdb | gzip > /root/image.gz

#文件大小為2.3k[Oracle@rhel6 ~]$ ll db1_db_links.sql -rw-r--r-- 1 oracle oinstall 2344 Nov 21 10:39 db1_db_links.sql#把這個文件拆成每個文件1k，bs=1k，count=1，使用skip參數指定在輸入文件中跳過多少個bs支讀取[oracle@rhel6 ~]$ 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[oracle@rhel6 ~]$ 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[oracle@rhel6 ~]$ 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#拆分出的文件[oracle@rhel6 ~]$ 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

#合并操作，此時用到seek參數，用于指定在輸入文件中跳過的bs數[oracle@rhel6 ~]$ 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[oracle@rhel6 ~]$ dd of=1.sql if=dd02.sql bs=1k seek=11+0 records in1+0 records out1024 bytes (1.0 kB) copied, 0.000124038 s, 8.3 MB/s[oracle@rhel6 ~]$ 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#與拆分前的文件進行校驗[oracle@rhel6 ~]$ diff 1.sql db1_db_links.sql[oracle@rhel6 ~]$

[oracle@rhel6 ~]$ dd if=2.sql of=1.sql bs=1k seek=1 count=2 conv=notrunc