---
name: "sd_journal_stream_fd"
section: "3"
platform: "linux"
package: "systemd-libs"
version: "262.1-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/sd_journal_stream_fd"
---

# sd\_journal\_stream\_fd(3)

Create log stream file descriptor to the journal

## NAME

sd\_journal\_stream\_fd, sd\_journal\_stream\_fd\_with\_namespace - Create log stream file descriptor to the journal

## SYNOPSIS

```
#include <systemd/sd-journal.h>
```

**int sd\_journal\_stream\_fd(const char \****identifier***, int** *priority***, int** *level\_prefix***);**

**int sd\_journal\_stream\_fd\_with\_namespace(const char \****name\_space***, const char \****identifier***, int** *priority***, int** *level\_prefix***);**

## DESCRIPTION

**sd\_journal\_stream\_fd()** may be used to create a log stream file descriptor. Log messages written to this file descriptor as simple newline-separated text strings are written to the journal. This file descriptor can be used internally by applications or be made standard output or standard error of other processes executed.

**sd\_journal\_stream\_fd()** takes a short program identifier string as first argument, which will be written to the journal as SYSLOG\_IDENTIFIER= field for each log entry (see [**systemd.journal-fields**(7)](/systemd.journal-fields/7.md) for more information). The second argument shall be the default priority level for all messages. The priority level is one of **LOG\_EMERG**, **LOG\_ALERT**, **LOG\_CRIT**, **LOG\_ERR**, **LOG\_WARNING**, **LOG\_NOTICE**, **LOG\_INFO**, **LOG\_DEBUG**, as defined in syslog.h, see [**syslog**(3)](/syslog/3.md) for details. The third argument is a boolean: if true kernel-style log level prefixes (such as **SD\_WARNING**) are interpreted, see [**sd-daemon**(3)](/sd-daemon/3.md) for more information.

**sd\_journal\_stream\_fd\_with\_namespace()** is similar to **sd\_journal\_stream\_fd()**, but takes an additional *name\_space* parameter that specifies which journal namespace to operate on. If specified as **NULL** the call is identical to **sd\_journal\_stream\_fd()**. For details about journal namespaces, see [**systemd-journald.service**(8)](/systemd-journald.service/8.md).

It is recommended that applications log UTF-8 messages only with this API, but this is not enforced.

Each invocation of these functions allocates a new log stream file descriptor, that is not shared with prior or later invocations. The file descriptor is write-only (its reading direction is shut down), and **O\_NONBLOCK** is turned off initially.

## RETURN VALUE

The call returns a valid write-only file descriptor on success or a negative errno-style error code.

## SIGNAL SAFETY

**sd\_journal\_stream\_fd()** and **sd\_journal\_stream\_fd\_with\_namespace()** are "async signal safe" in the meaning of [**signal-safety**(7)](/signal-safety/7.md).

## NOTES

All functions listed here are thread-safe and may be called in parallel from multiple threads.

Functions described here are available as a shared library, which can be compiled against and linked to with the **libsystemd** [**pkg-config**(1)](/pkg-config/1.md) file.

## EXAMPLES

Creating a log stream suitable for [**fprintf**(3)](/fprintf/3.md):

```
/* SPDX-License-Identifier: MIT-0 */
#define _GNU_SOURCE 1
#include <errno.h>
#include <syslog.h>
#include <stdio.h>
#include <unistd.h>
#include <systemd/sd-journal.h>
#include <systemd/sd-daemon.h>
int main(int argc, char *argv[]) {
  int fd;
  FILE *log;
  fd = sd_journal_stream_fd("test", LOG_INFO, 1);
  if (fd < 0) {
    fprintf(stderr, "Failed to create stream fd: %s\n", strerror(-fd));
    return 1;
  }
  log = fdopen(fd, "w");
  if (!log) {
    fprintf(stderr, "Failed to create file object: %s\n", strerror(errno));
    close(fd);
    return 1;
  }
  fprintf(log, "Hello World!\n");
  fprintf(log, SD_WARNING "This is a warning!\n");
  fclose(log);
  return 0;
}
```

## HISTORY

**sd\_journal\_stream\_fd()** was added in version 187.

**sd\_journal\_stream\_fd\_with\_namespace()** was added in version 256.

## SEE ALSO

[**systemd**(1)](/systemd/1.md), [**sd-journal**(3)](/sd-journal/3.md), [**sd-daemon**(3)](/sd-daemon/3.md), [**sd\_journal\_print**(3)](/sd_journal_print/3.md), [**syslog**(3)](/syslog/3.md), [**fprintf**(3)](/fprintf/3.md), [**systemd.journal-fields**(7)](/systemd.journal-fields/7.md)