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132 lines
5.2 KiB
Groff
132 lines
5.2 KiB
Groff
'\" t
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.TH "SD_JOURNAL_QUERY_UNIQUE" "3" "" "systemd 219" "sd_journal_query_unique"
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.\" -----------------------------------------------------------------
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.\" * Define some portability stuff
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.\" -----------------------------------------------------------------
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.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.\" http://bugs.debian.org/507673
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.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
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.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.ie \n(.g .ds Aq \(aq
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.el .ds Aq '
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.\" -----------------------------------------------------------------
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.\" * set default formatting
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.\" -----------------------------------------------------------------
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.\" disable hyphenation
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.nh
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.\" disable justification (adjust text to left margin only)
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.ad l
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.\" -----------------------------------------------------------------
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.\" * MAIN CONTENT STARTS HERE *
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.\" -----------------------------------------------------------------
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.SH "NAME"
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sd_journal_query_unique, sd_journal_enumerate_unique, sd_journal_restart_unique, SD_JOURNAL_FOREACH_UNIQUE \- Read unique data fields from the journal
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.SH "SYNOPSIS"
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.sp
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.ft B
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.nf
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#include <systemd/sd\-journal\&.h>
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.fi
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.ft
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.HP \w'int\ sd_journal_query_unique('u
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.BI "int sd_journal_query_unique(sd_journal\ *" "j" ", const\ char\ *" "field" ");"
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.HP \w'int\ sd_journal_enumerate_unique('u
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.BI "int sd_journal_enumerate_unique(sd_journal\ *" "j" ", const\ void\ **" "data" ", size_t\ *" "length" ");"
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.HP \w'void\ sd_journal_restart_unique('u
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.BI "void sd_journal_restart_unique(sd_journal\ *" "j" ");"
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.HP \w'SD_JOURNAL_FOREACH_UNIQUE('u
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.BI "SD_JOURNAL_FOREACH_UNIQUE(sd_journal\ *" "j" ", const\ void\ *" "data" ", size_t\ " "length" ");"
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.SH "DESCRIPTION"
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.PP
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\fBsd_journal_query_unique()\fR
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queries the journal for all unique values the specified field can take\&. It takes two arguments: the journal to query and the field name to look for\&. Well\-known field names are listed on
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\fBsystemd.journal-fields\fR(7)\&. Field names must be specified without a trailing \*(Aq=\*(Aq\&. After this function has been executed successfully the field values may be queried using
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\fBsd_journal_enumerate_unique()\fR\&. Invoking this call a second time will change the field name being queried and reset the enumeration index to the first field value that matches\&.
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.PP
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\fBsd_journal_enumerate_unique()\fR
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may be used to iterate through all data fields which match the previously selected field name as set with
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\fBsd_journal_query_unique()\fR\&. On each invocation the next field data matching the field name is returned\&. The order of the returned data fields is not defined\&. It takes three arguments: the journal context object, plus a pair of pointers to pointer/size variables where the data object and its size shall be stored in\&. The returned data is in a read\-only memory map and is only valid until the next invocation of
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\fBsd_journal_enumerate_unique()\fR\&. Note that the data returned will be prefixed with the field name and \*(Aq=\*(Aq\&. Note that this call is subject to the data field size threshold as controlled by
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\fBsd_journal_set_data_threshold()\fR\&.
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.PP
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\fBsd_journal_restart_unique()\fR
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resets the data enumeration index to the beginning of the list\&. The next invocation of
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\fBsd_journal_enumerate_unique()\fR
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will return the first field data matching the field name again\&.
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.PP
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Note that the
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\fBSD_JOURNAL_FOREACH_UNIQUE()\fR
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macro may be used as a handy wrapper around
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\fBsd_journal_restart_unique()\fR
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and
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\fBsd_journal_enumerate_unique()\fR\&.
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.PP
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Note that these functions currently are not influenced by matches set with
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\fBsd_journal_add_match()\fR
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but this might change in a later version of this software\&.
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.SH "RETURN VALUE"
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.PP
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\fBsd_journal_query_unique()\fR
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returns 0 on success or a negative errno\-style error code\&.
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\fBsd_journal_enumerate_unique()\fR
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returns a positive integer if the next field data has been read, 0 when no more fields are known, or a negative errno\-style error code\&.
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\fBsd_journal_restart_unique()\fR
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returns nothing\&.
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.SH "NOTES"
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.PP
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The
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\fBsd_journal_query_unique()\fR,
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\fBsd_journal_enumerate_unique()\fR
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and
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\fBsd_journal_restart_unique()\fR
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interfaces are available as a shared library, which can be compiled and linked to with the
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\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
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file\&.
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.SH "EXAMPLES"
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.PP
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Use the
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\fBSD_JOURNAL_FOREACH_UNIQUE\fR
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macro to iterate through all values a field of the journal can take\&. The following example lists all unit names referenced in the journal:
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.sp
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.if n \{\
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.RS 4
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.\}
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.nf
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#include <stdio\&.h>
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#include <string\&.h>
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#include <systemd/sd\-journal\&.h>
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int main(int argc, char *argv[]) {
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sd_journal *j;
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const void *d;
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size_t l;
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int r;
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r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
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if (r < 0) {
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fprintf(stderr, "Failed to open journal: %s\en", strerror(\-r));
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return 1;
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}
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r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
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if (r < 0) {
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fprintf(stderr, "Failed to query journal: %s\en", strerror(\-r));
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return 1;
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}
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SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
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printf("%\&.*s\en", (int) l, (const char*) d);
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sd_journal_close(j);
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return 0;
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}
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.fi
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.if n \{\
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.RE
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.\}
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.SH "SEE ALSO"
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.PP
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\fBsystemd\fR(1),
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\fBsystemd.journal-fields\fR(7),
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\fBsd-journal\fR(3),
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\fBsd_journal_open\fR(3),
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\fBsd_journal_get_data\fR(3),
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\fBsd_journal_add_match\fR(3)
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