ERR(3) | Library Functions Manual | ERR(3)

# NAME

`ERR` — OpenSSL error codes

# SYNOPSIS

library “libcrypto”
`#include <openssl/err.h>`

# DESCRIPTION

When a call to the OpenSSL library fails, this is usually signaled by the return value, and an error code is stored in an error queue associated with the current thread. The `ERR` library provides functions to obtain these error codes and textual error messages. The ERR_get_error(3) manpage describes how to access error codes.

Error codes contain information about where the error occurred, and what went wrong. ERR_GET_LIB(3) describes how to extract this information. A method to obtain human-readable error messages is described in ERR_error_string(3).

ERR_clear_error(3) can be used to clear the error queue.

Note that ERR_remove_state(3) should be used to avoid memory leaks when threads are terminated.

# ADDING NEW ERROR CODES TO OPENSSL

See ERR_put_error(3) if you want to record error codes in the OpenSSL error system from within your application.

The remainder of this section is of interest only if you want to add new error codes to OpenSSL or add error codes from external libraries.

When you are using new function or reason codes, run make errors. The necessary #defines will then automatically be added to the sub-library's header file.

## Adding new libraries

When adding a new sub-library to OpenSSL, assign it a library number `ERR_LIB_XXX`, define a macro `XXXerr`() (both in `<openssl/err.h>`), add its name to ERR_str_libraries[] (in /usr/src/lib/libcrypto/err/err.c), and add `ERR_load_XXX_strings`() to the `ERR_load_crypto_strings`() function (in /usr/src/lib/libcrypto/err/err_all.c). Finally, add xxx_err.c to the Makefile.

# USING ERROR CODES IN EXTERNAL LIBRARIES

It is also possible to use OpenSSL's error code scheme in external libraries.

# INTERNALS

The error queues are stored in a hash table with one ERR_STATE entry for each PID. `ERR_get_state`() returns the current thread's ERR_STATE. An ERR_STATE can hold up to `ERR_NUM_ERRORS` error codes. When more error codes are added, the old ones are overwritten, on the assumption that the most recent errors are most important.

Error strings are also stored in a hash table.

# SEE ALSO

crypto(3), ERR_asprintf_error_data(3), ERR_clear_error(3), ERR_error_string(3), ERR_get_error(3), ERR_GET_LIB(3), ERR_load_crypto_strings(3), ERR_load_strings(3), ERR_print_errors(3), ERR_put_error(3), ERR_remove_state(3), ERR_set_mark(3), SSL_get_error(3)

June 8, 2025 | Debian