OPENSSL-REHASH(1)

NAME
openssl-rehash, c_rehash - Create symbolic links to files named by the hash values

SYNOPSIS
openssl rehash [-h] [-help] [-old] [-compat] [-n] [-v] [-provider name] [-provider-path path] [-provparam [name:]key=value] [-propquery propq] [directory] ...

DESCRIPTION
openssl 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 command 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 a directory is processed, all links in it that have a name in that syntax are first removed, even if they are being used for some other purpose. 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 or if more than one such object appears in the file.

OPTIONS

-help -h
    Display a brief usage message.

-old
    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.

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

-compat
    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 releases.

-v  Print messages about old links removed and new links created. By default, this command only lists each directory as it is processed.

-provider name
-provider-path path
-provparam [name:]key=value
-propquery propq
    See "Provider Options" in openssl(1), provider(7), and property(7).

ENVIRONMENT

OPENSSL
    The path to an executable to use to generate hashes and fingerprints (see above).

PATH
    List of paths, separated by colons (or semicolons, on Windows platforms), where the openssl executable is searched in case the path to the hash generating executable is not provided in the OPENSSL environment variable or it is not usable (that is, does not exist or is not executable).

SSL_CERT_DIR
    List of directories to operate on. On Unix-like systems the list entries are separated by a colon. On Windows they are separated by a semicolon. Ignored if directories are listed on the command line.

SEE ALSO
openssl(1), openssl-crl(1), openssl-x509(1)

HISTORY
c_rehash was removed in OpenSSL 4.0. Use openssl rehash instead.

COPYRIGHT
Copyright 2015-2026 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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 <https://www.openssl.org/source/license.html>.