1, Introduction
MD5Algorithms are generally used to check file integrity, and are especially often used to detect the correctness of files in the case of (network) file transfer, copying, disk errors or other cases without malicious involvement.MD5Full nameMessage Digest Algorithm（Message-DigestAlgorithm 5）[RFC 1321], The algorithm performs bit-by-bit calculation of information of any length to generate a binary length128Bits (hexadecimal length32The probability of generating the same message digest from different file contents is extremely small.
existLinuxorUnixsuperior,md5sumIt is a tool program used to calculate and verify file message digests. Generally speaking, installedLinuxAfter that, there will bemd5sumTools can be executed directly on the command line terminal.
2, command format
md5sum [OPTION]... [FILE]...
Command Options
-bor --binary:Read into the file in binary mode;
-tor --text:Read the file in text file mode (default);
-cor --check:Used to read from a filemd5Information checks the consistency of files;
--status:The option ischeckUse together, incheckWhen not output, the check result is represented according to the return value;
-wor --warn:existcheckWhen checking the inputmd5Is there any illegal information? If there is any, the corresponding information will be output.
4, example demonstration
1) generate a filemd5The value is as follows:
[root@HLZ test]# ll
total 16
-rw-r--r--1 root root 240 Sep 4 22:26 aaa_pkg.tgz
-rw-r--r--1 root root 11 Sep 4 22:01
-rw-r--r--1 root root 46 Sep 4 22:24
drwxr-xr-x2 root root 4096 Sep 4 22:24 checksum
[root@HLZ test]#
[root@HLZ test]# md5sum > checksum/aaa.md5
In this way, the file is generatedofmd5Verify filesaaa.md5，Open it and you can see the following content:
[root@HLZ test]# cat checksum/aaa.md5
d700cf9bb133858df4d3e0486848be78
2）md5sumSupports multiple file inputs or wildcards
[root@HLZ test]# md5sum aaa_pkg.tgz > checksum/all.md5
[root@HLZ test]# cat checksum/all.md5
d700cf9bb133858df4d3e0486848be78
fff62b77988e5b9d83a2872bb2247b21
36eb58b2563f91baf61531aef126eea6 aaa_pkg.tgz
[root@HLZ test]# md5sum aaa* > checksum/aaa_all.md5
[root@HLZ test]# cat checksum/aaa_all.md5
36eb58b2563f91baf61531aef126eea6 aaa_pkg.tgz
d700cf9bb133858df4d3e0486848be78
3) File content verification
[root@HLZ test]# md5sum -c ./checksum/aaa.md5
:OK
[root@HLZ test]# md5sum -c ./checksum/all.md5
:OK
:OK
aaa_pkg.tgz:OK
[root@HLZ test]# vi ---ReviseFile content, add7indivual0
abceefghijklmnopqr0000000stuvwxyz1234567890987654321
[root@HLZ test]# md5sum -c ./checksum/all.md5
:OK
: FAILED
aaa_pkg.tgz:OK
md5sum: WARNING: 1 of 3 computed checksums did NOT match
[root@HLZ test]#
4) Consideration of file path ($PWDThat is, the current path/home/hanlzh/test/）
[root@HLZ test]# pwd
/home/hanlzh/test
[root@HLZ test]# md5sum $PWD/ > ./checksum/aaa.md5
[root@HLZ test]# cat checksum/aaa.md5
d700cf9bb133858df4d3e0486848be78 /home/hanlzh/test/
[root@HLZ test]# md5sum -c ./checksum/aaa.md5
/home/hanlzh/test/:OK
[root@HLZ test]# cd ..
[root@HLZ hanlzh]# md5sum -c ./test/checksum/aaa.md5
/home/hanlzh/test/:OK
4) File missing or not exists
[root@HLZ test]# rm -rf aaa_pkg.tgz
[root@HLZ test]# md5sum -c ./checksum/aaa_all.md5
md5sum: aaa_pkg.tgz: No such file or directory
aaa_pkg.tgz: FAILED open or read
:OK
md5sum: WARNING: 1 of 2 listed files could not be read
5,Summarize
Special Instructions
1）md5sumIt is to verify the content of the file, and it has nothing to do with whether the file name is the same;
2）md5sumIt is bit-by-bit verification, so the larger the file, the longer the verification time.
md5Check, there may be a very small probability that different files will generate the same checksum,md5Safer verificationalgorithmbesidesSHA*Series, such assha1sum/sha224sum/sha256sum/sha384sum/sha512sumSo, basic usage andmd5sumThe command is similar, details can be passedman sha1sumQuery.
The following is a brief example and will not be repeated.
[root@HLZ test]# sha512sum > aaa.sha512
[root@HLZ test]# cat aaa.sha512
8edb9790359ef641112fa85eea5c8f09b7330564a58cddf39aef66006f32454a8879b1e63d9f667ecf86264d4d5b6a602a4c94c79d962ec755345a3837217f89
[root@HLZ test]#
[root@HLZ test]# sha512sum -c ./aaa.sha512
:OK