sd_journal_stream_fd(3) [centos man page]
SD_JOURNAL_STREAM_FD(3) sd_journal_stream_fd SD_JOURNAL_STREAM_FD(3) NAME
sd_journal_stream_fd - 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); 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 STDOUT/STDERR 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) 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) for details. The third argument is a boolean: if true kernel-style log priority level prefixes (such as SD_WARNING) are interpreted, see sd-daemon(3) for more information. It is recommended that applications log UTF-8 messages only with this API, but this is not enforced. RETURN VALUE
The call returns a valid write-only file descriptor on success or a negative errno-style error code. NOTES
The sd_journal_stream_fd() interface is available as a shared library, which can be compiled and linked to with the libsystemd-journal pkg- config(1) file. EXAMPLES
Creating a log stream suitable for fprintf(3): #include <syslog.h> #include <stdio.h> #include <string.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 ", strerror(-fd)); return 1; } log = fdopen(fd, "w"); if (!log) { fprintf(stderr, "Failed to create file object: %m "); close(fd); return 1; } fprintf(log, "Hello World! "); fprintf(log, SD_WARNING "This is a warning! "); fclose(log); return 0; } SEE ALSO
systemd(1), sd-journal(3), sd-daemon(3), sd_journal_print(3), syslog(3), fprintf(3), systemd.journal-fields(7) systemd 208 SD_JOURNAL_STREAM_FD(3)
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SYSTEMD-JOURNALD.SERVICE(8) systemd-journald.service SYSTEMD-JOURNALD.SERVICE(8) NAME
systemd-journald.service, systemd-journald.socket, systemd-journald - Journal service SYNOPSIS
systemd-journald.service systemd-journald.socket /usr/lib/systemd/systemd-journald DESCRIPTION
systemd-journald is a system service that collects and stores logging data. It creates and maintains structured, indexed journals based on logging information that is received from the kernel, from user processes via the libc syslog(3) call, from STDOUT/STDERR of system services or via its native API. It will implicitly collect numerous meta data fields for each log messages in a secure and unfakeable way. See systemd.journal-fields(7) for more information about the collected meta data. Log data collected by the journal is primarily text-based but can also include binary data where necessary. All objects stored in the journal can be up to 2^64-1 bytes in size. By default, the journal stores log data in /run/log/journal/. Since /run/ is volatile, log data is lost at reboot. To make the data persistent, it is sufficient to create /var/log/journal/ where systemd-journald will then store the data. systemd-journald will forward all received log messages to the AF_UNIXSOCK_DGRAM socket /run/systemd/journal/syslog, if it exists, which may be used by Unix syslog daemons to process the data further. See journald.conf(5) for information about the configuration of this service. SIGNALS
SIGUSR1 Request that journal data from /run/ is flushed to /var/ in order to make it persistent (if this is enabled). This must be used after /var/ is mounted, as otherwise log data from /run is never flushed to /var regardless of the configuration. SIGUSR2 Request immediate rotation of the journal files. KERNEL COMMAND LINE
A few configuration parameters from journald.conf may be overridden on the kernel command line: systemd.journald.forward_to_syslog=, systemd.journald.forward_to_kmsg=, systemd.journald.forward_to_console= Enables/disables forwarding of collected log messages to syslog, the kernel log buffer or the system console. See journald.conf(5) for information about these settings. ACCESS CONTROL
Journal files are, by default, owned and readable by the "systemd-journal" system group but are not writable. Adding a user to this group thus enables her/him to read the journal files. By default, each logged in user will get her/his own set of journal files in /var/log/journal/. These files will not be owned by the user, however, in order to avoid that the user can write to them directly. Instead, file system ACLs are used to ensure the user gets read access only. Additional users and groups may be granted access to journal files via file system access control lists (ACL). Distributions and administrators may choose to grant read access to all members of the "wheel" and "adm" system groups with a command such as the following: # setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/ Note that this command will update the ACLs both for existing journal files and for future journal files created in the /var/log/journal/ directory. FILES
/etc/systemd/journald.conf Configure systemd-journald behaviour. See journald.conf(5). /run/log/journal/machine-id/*.journal, /run/log/journal/machine-id/*.journal~, /var/log/journal/machine-id/*.journal, /var/log/journal/machine-id/*.journal~ systemd-journald writes entries to files in /run/log/journal/machine-id/ or /var/log/journal/machine-id/ with the ".journal" suffix. If the daemon is stopped uncleanly, or if the files are found to be corrupted, they are renamed using the ".journal~" suffix, and systemd-journald starts writing to a new file. /run is used when /var/log/journal is not available, or when Storage=volatile is set in the journald.conf(5) configuration file. SEE ALSO
systemd(1), journalctl(1), journald.conf(5), systemd.journal-fields(7), sd-journal(3), setfacl(1), pydoc systemd.journal. systemd 208 SYSTEMD-JOURNALD.SERVICE(8)