csum Command

Purpose

The csum command calculates a message digest for the specified files using the specified hash algorithm.

Syntax

csum [-o outputfile] [-h algorithm] [-a] [File1, File2, ... | - ]

csum -i inputfile[-h algorithm]

Description

The csum command calculates a message digest for the specified files using the specified hash algorithm. This provides a reliable way to verify file integrity.

The csum command writes message digests to a specified file which can later be used to verify file integrity. Note that a file can be specified using absolute or relative path names.

Specifying multiple -i, -o or -h flags is not considered an error; the last instance of the flag specified will be used. However, it is an error to use both the -i and -o flags at the same time.

Flags

Item	Description
-	Specifies input from stdin.
-a	Specifies that one message digest will be generated for all files.
-h algorithm	Specifies which hash algorithms the csum command will use to generate a message digest or verify the message digest values when using the -i option. The following options are available: SHA1: Uses the SHA-1 algorithm to generate a 20 byte message digest. MD5: Uses the MD5 algorithm to generate a 16 byte message digest. Note: these options are case sensitive. If this -h option is not used, then the csum command will default to using the MD5 algorithm for both generating and verifying message digests.
-i inputfile	Specifies an input file, generated by the -o flag, which contains trusted message-digest values. The csum command calculates the message-digest values of the files specified in the input file and verifies that they match the actual message-digest values of the existing file. The -h flag should be used with the -i flag to specify which cryptographic hash algorithm is used to generate the input file. If it is not specified, the MD5 algorithm will be used. If a file specified in the input file generates a message-digest value different than the value stored in the input file or the file does not exist, the test for that file will fail and the csum command will continue to process the files specified in the input file.
-o outputfile	Specifies an output file that the csum command will use to write message-digest values. This flag cannot be used with the -i flag. If the file specified already exists, it will be overwritten.

Exit Status

The command returns the following values:

Item	Description
0	Success.
>0	An error occurred.

Examples

To calculate the message digest for the files cars and trucks, type:
```
csum cars trucks
```
Because the -h option is not specified, MD5 values are calculated for the files cars and trucks.
If 9875DD0B18C15899988F29E9D85346A4 and E8C3ABB5E1D48FA519135EAB0FE40932 are the MD5 values for cars and trucks, respectively, the csum command outputs the following:
```
9875DD0B18C15899988F29E9D85346A4        cars
E8C3ABB5E1D48FA519135EAB0FE40932        trucks
```
To calculate the message digest for all files with file names beginning with file and store the output in a file called mdvalues, type:
```
 csum -o mdvalues file*
```
The output file, mdvalues, will contain the following text if the directory where the csum command is executed contains the files file1, file2, and file3 and the MD5 values for those files are as listed below:
```
B026324C6904B2A9CB4B88D6D61C81D1        file1
26AB0DB90D72E28AD0BA1E22EE510510        file2
D7FCE9FEE471194AA8B5B6E47267F03         file3
```
To verify that the message digests in the file mdvalues match the current message-digest values for those same files, type:
```
csum -i mdvalues
```
To calculate the message digest for the file user.dat using the SHA-1 algorithm, type:
```
csum -h SHA1 user.dat
```
If the SHA-1 value for the user.dat file is A77CBB748AC336558AFA1AE7F2B73F3765728E7B, the csum command will output the following:
```
A77CBB748AC336558AFA1AE7F2B73F3765728E7B        user.dat
```

Location

/usr/bin/csum