sd_journal_next() advances the read pointer into the journal by one
entry. The only argument taken is a journal context object as
allocated via sd_journal_open(3). After successful invocation the
entry may be read with functions such as sd_journal_get_data(3).
Similarly, sd_journal_previous() sets the read pointer back one
sd_journal_next_skip() and sd_journal_previous_skip() advance/set
back the read pointer by multiple entries at once, as specified in
the skip parameter.
The journal is strictly ordered by reception time, and hence
advancing to the next entry guarantees that the entry then pointing
to is later in time than then previous one, or has the same
Note that sd_journal_get_data(3) and related calls will fail unless
sd_journal_next() has been invoked at least once in order to position
the read pointer on a journal entry.
Note that the SD_JOURNAL_FOREACH() macro may be used as a wrapper
around sd_journal_seek_head(3) and sd_journal_next() in order to make
iterating through the journal easier. See below for an example.
Similarly, SD_JOURNAL_FOREACH_BACKWARDS() may be used for iterating
the journal in reverse order.
The four calls return the number of entries advanced/set back on
success or a negative errno-style error code. When the end or
beginning of the journal is reached, a number smaller than requested
is returned. More specifically, if sd_journal_next() or
sd_journal_previous() reach the end/beginning of the journal they
will return 0, instead of 1 when they are successful. This should be
considered an EOF marker.
The sd_journal_next(), sd_journal_previous(), sd_journal_next_skip()
and sd_journal_previous_skip() interfaces are available as a shared
library, which can be compiled and linked to with the
libsystemd pkg-config(1) file.
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project. Information about the project can be found at
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systemd 231 SD_JOURNAL_NEXT(3)