c_rehash Man page



c_rehash – Create symbolic links to files named by the hash values


c_rehash [-old] [-h] [-n] [-v] [ directory…]


c_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

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 shold 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 it will be skipped. 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, c_rehash will first remove all links that have a name in
that syntax. If you have links in that format used for other purposes,
they will be removed. 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 is found.

A warning will also be displayed if there are files that cannot be
parsed as either a certificate or a CRL.

The program uses the openssl program to compute the hashes and
fingerprints. If not found in the user’s PATH, then set the OPENSSL
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 FILE


$OPENSSL crl -hash -fingerprint -noout -in FILE


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.


Use old-style hashing (MD5, as opposed to SHA-1) for generating
links for releases before 1.0.0. Note that current versions will
not use the old style.

-h Display a brief usage message.

-n Do not remove existing links. This is needed when keeping new and
old-style links in the same directory.

-v Print messages about old links removed and new links created. By
default, c_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.


openssl, crl(1). x509(1).

1.0.2g 2016-03-01 C_REHASH(1SSL)