The dd command in Linux USES an example tutorial
- 2020-06-07 05:56:04
- OfStack
This paper mainly introduces the use of dd command in Linux and shares it for your reference and study. Here is a detailed introduction:
1. The Linux dd command copies a file with a block of the specified size and performs the specified conversion while copying.
Usage:
dd [OPERAND]
Parameter notes:
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( The 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( The default is 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 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: The specified number is multiplied by the corresponding number if it ends in the following character:
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
2. Use examples
1. Backup the local /dev/hdb disk to /dev/hdd
dd if=/dev/hdb of=/dev/hdd
2. Backup all /dev/hdb data to the image file in the specified path
dd if=/dev/hdb of=/root/image
3. Backup /dev/hdb data and use gzip tools to compress and save to the specified path
dd if=/dev/hdb | gzip > /root/image.gz
4. Split 1 file into 3 files
# File size is 2.3k
[Oracle@rhel6 ~]$ ll db1_db_links.sql
-rw-r--r-- 1 oracle oinstall 2344 Nov 21 10:39 db1_db_links.sql
# Break this file into each one 1k . bs=1k . count=1 , the use of skip Parameter specifies how many to skip in the input file bs A read
[oracle@rhel6 ~]$ dd if=db1_db_links.sql of=dd01.sql bs=1k count=1
1+0 records in
1+0 records out
1024 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=1
1+0 records in
1+0 records out
1024 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=2
0+1 records in
0+1 records out
296 bytes (296 B) copied, 0.000204216 s, 1.4 MB/s
# Split out the file
[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
5. Merge the split files into one
# Merge operation, in this case seek Parameter to specify which to skip in the input file bs The number
[oracle@rhel6 ~]$ dd of=1.sql if=dd01.sql
2+0 records in
2+0 records out
1024 bytes (1.0 kB) copied, 0.000176 s, 5.8 MB/s
[oracle@rhel6 ~]$ dd of=1.sql if=dd02.sql bs=1k seek=1
1+0 records in
1+0 records out
1024 bytes (1.0 kB) copied, 0.000124038 s, 8.3 MB/s
[oracle@rhel6 ~]$ dd of=1.sql if=dd03.sql bs=1k seek=2
0+1 records in
0+1 records out
296 bytes (296 B) copied, 0.00203881 s, 145 kB/s
# Verify with the file before the split
[oracle@rhel6 ~]$ diff 1.sql db1_db_links.sql
[oracle@rhel6 ~]$
6. Inserts data at the location specified in the output file without truncating the output file
You need to use
conv=notrunc
parameter
[oracle@rhel6 ~]$ dd if=2.sql of=1.sql bs=1k seek=1 count=2 conv=notrunc
conclusion