Section: OpenSSL (1)
openssl-c_rehash, openssl-rehash, c_rehash, rehash - Create symbolic links to files named by the hash values
On some platforms, the OpenSSL rehash
command is available as
an external script called c_rehash
. They are functionally equivalent,
except for minor differences noted below.
rehash scans directories and calculates a hash value of each
".pem", ".crt", ".cer", or ".crl"
file in the specified directory list and creates symbolic links
for each file, where the name of the link is the hash value.
(If the platform does not support symbolic links, a copy is made.)
This utility is useful as many programs that use OpenSSL require
directories to be set up like this in order to find certificates.
If any directories are named on the command line, then those are
processed in turn. If not, then the SSL_CERT_DIR environment variable
is consulted; this should be a colon-separated list of directories,
like the Unix PATH variable.
If that is not set then the default directory (installation-specific
but often /usr/local/ssl/certs) is processed.
In order for a directory to be processed, the user must have write
permissions on that directory, otherwise an error will be generated.
The links created are of the form "HHHHHHHH.D", where each H
is a hexadecimal character and D is a single decimal digit.
When processing a directory, rehash will first remove all links
that have a name in that syntax, even if they are being used for some
To skip the removal step, use the -n flag.
Hashes for CRL's look similar except the letter r appears after
the period, like this: "HHHHHHHH.rD".
Multiple objects may have the same hash; they will be indicated by
incrementing the D value. Duplicates are found by comparing the
full SHA-1 fingerprint. A warning will be displayed if a duplicate
A warning will also be displayed if there are files that
cannot be parsed as either a certificate or a CRL or if
more than one such object appears in the file.
uses the openssl
program to compute the hashes and
fingerprints. If not found in the user's PATH
, then set the
environment variable to the full pathname.
Any program can be used, it will be invoked as follows for either
a certificate or CRL:
$OPENSSL x509 -hash -fingerprint -noout -in FILENAME
$OPENSSL crl -hash -fingerprint -noout -in FILENAME
where FILENAME is the filename. It must output the hash of the
file on the first line, and the fingerprint on the second,
optionally prefixed with some text and an equals sign.
- -help -h
Display a brief usage message.
Use old-style hashing (MD5, as opposed to SHA-1) for generating
links to be used for releases before 1.0.0.
Note that current versions will not use the old style.
Do not remove existing links.
This is needed when keeping new and old-style links in the same directory.
Generate links for both old-style (MD5) and new-style (SHA1) hashing.
This allows releases before 1.0.0 to use these links along-side newer
Print messages about old links removed and new links created.
By default, rehash only lists each directory as it is processed.
The path to an executable to use to generate hashes and
fingerprints (see above).
Colon separated list of directories to operate on.
Ignored if directories are listed on the command line.
Copyright 2015-2018 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the ``License''). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at