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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |NOTES |EXAMPLES |HISTORY |SEE ALSO |COLOPHON | |
SD_HWDB_GET(3) sd_hwdb_getSD_HWDB_GET(3)sd_hwdb_get, sd_hwdb_seek, sd_hwdb_enumerate, SD_HWDB_FOREACH_PROPERTY - Seek to a location in hwdb or access entries
#include <systemd/sd-hwdb.h>int sd_hwdb_get(sd_hwdb *hwdb, const char *modalias,const char *key, const char **value);int sd_hwdb_seek(sd_hwdb *hwdb, const char *modalias);int sd_hwdb_enumerate(sd_hwdb *hwdb, const char **key,const char **value);SD_HWDB_FOREACH_PROPERTY(hwdb, modalias, key, value);
sd_hwdb_get()queries thehwdb object created earlier withsd_hwdb_new(3) for entries matching the specified stringmodalias, and returns the value corresponding to the keykey. The value is returned as aNUL-terminated string invalue. It must not be modified by the caller and is valid as long as a reference tohwdb is kept. When multiple patterns in the database matchmodalias, the one with the highest priority is used. Seehwdb(7) for details.sd_hwdb_seek()selects entries matching the specified stringmodalias. Subsequent queries withsd_hwdb_enumerate()will access the key-value pairs for that string.sd_hwdb_enumerate()returns (in turn) all the key-value pairs defined for the string used withsd_hwdb_seek(). Each pair is returned asNUL-terminated strings inkey andvalue. The strings must not be modified by the caller and are valid as long as a reference tohwdb is kept. When multiple patterns in the database matchmodalias, the combination of all matching key-value pairs is used. Seehwdb(7) for details. TheSD_HWDB_FOREACH_PROPERTY()macro combinessd_hwdb_seek()andsd_hwdb_enumerate(). No error handling is performed and iteration simply stops on error. See the example below.
On success,sd_hwdb_get()andsd_hwdb_seek()return a non-negative integer. On failure, they return a negative errno-style error code.sd_hwdb_enumerate()returns a positive integer if another key-value pair was found or zero if all entries have already been enumerated. On failure, it returns a negative errno-style error code.Errors Returned errors may indicate the following problems:-EINVAL A parameter isNULL. Added in version 246.-ENOENT An entry for the specifiedmodalias was not found. Added in version 246.-EAGAINsd_hwdb_seek()was not called beforesd_hwdb_enumerate(). Added in version 246.
Functions described here are available as a shared library, which can be compiled against and linked to with thelibsystemd pkg-config(1) file. The code described here usesgetenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not callsetenv(3) from a parallel thread. It is recommended to only do calls tosetenv()from an early phase of the program when no other threads have been started.
Example 1. Look up hwdb entries for a USB device /* SPDX-License-Identifier: MIT-0 */ #define _GNU_SOURCE 1 #include <stdio.h> #include <stdint.h> #include <systemd/sd-hwdb.h> int print_usb_properties(uint16_t vid, uint16_t pid) { char match[128]; sd_hwdb *hwdb; const char *key, *value; int r; /* Match this USB vendor and product ID combination */ snprintf(match, sizeof match, "usb:v%04Xp%04X", vid, pid); r = sd_hwdb_new(&hwdb); if (r < 0) return r; SD_HWDB_FOREACH_PROPERTY(hwdb, match, key, value) printf("%s: \"%s\" → \"%s\"\n", match, key, value); sd_hwdb_unref(hwdb); return 0; } int main(int argc, char **argv) { print_usb_properties(0x046D, 0xC534); return 0; } The effect is similar to callingsystemd-hwdb queryusb:v046DpC534.sd_hwdb_get(),sd_hwdb_seek(),sd_hwdb_enumerate(), andSD_HWDB_FOREACH_PROPERTY()were added in version 246.
systemd(1),systemd-udevd.service(8),sd-hwdb(3),systemd-hwdb(8)
This page is part of thesystemd (systemd system and service manager) project. Information about the project can be found at ⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug report for this manual page, see ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This page was obtained from the project's upstream Git repository ⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that time, the date of the most recent commit that was found in the repository was 2025-08-11.) If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up-to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgsystemd 258~rc2SD_HWDB_GET(3)Pages that refer to this page:sd-hwdb(3), sd_hwdb_new(3), systemd.directives(7), systemd.index(7)
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