linux dd 读取文件命令

linux dd 读取系统文件生成指定大小文件

dd if=/dev/zero of=sun.txt bs=4096M count=1

dd详解

Usage: dd [OPERAND]...  or:  dd OPTIONCopy a file, converting and formatting according to the operands.  bs=BYTES        read and write up to BYTES bytes at a time  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 up to BYTES bytes at a time (default: 512)  if=FILE         read from FILE instead of stdin  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  oflag=FLAGS     write as per the comma separated symbol list  seek=N          skip N obs-sized blocks at start of output  skip=N          skip N ibs-sized blocks at start of input  status=LEVEL    The LEVEL of information to print to stderr;                  'none' suppresses everything but error messages,                  'noxfer' suppresses the final transfer statistics,                  'progress' shows periodic transfer statisticsN and BYTES may be followed by the following multiplicative suffixes: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.Each CONV symbol may be:  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  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  sync      pad every input block with NULs to ibs-size; when used            with block or unblock, pad with spaces rather than NULs  excl      fail if the output file already exists  nocreat   do not create the output file  notrunc   do not truncate the output file  noerror   continue after read errors  fdatasync  physically write output file data before finishing  fsync     likewise, but also write metadataEach FLAG symbol may be:  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  nocache   Request to drop cache.  See also oflag=sync  noctty    do not assign controlling terminal from file  nofollow  do not follow symlinks  count_bytes  treat 'count=N' as a byte count (iflag only)  skip_bytes  treat 'skip=N' as a byte count (iflag only)  seek_bytes  treat 'seek=N' as a byte count (oflag only)Sending a USR1 signal to a running 'dd' process makes itprint I/O statistics to standard error and then resume copying.Options are:      --help     display this help and exit      --version  output version information and exit