# sd_journal_get_data

## NAME



           sd_journal_get_data, sd_journal_enumerate_data,
           sd_journal_enumerate_available_data, sd_journal_restart_data,
           SD_JOURNAL_FOREACH_DATA, sd_journal_set_data_threshold,
           sd_journal_get_data_threshold - Read data fields from the current
           journal entry
    


## SYNOPSIS



           **#include <systemd/sd-journal.h>**
    
           **int sd_journal_get_data(sd_journal ***_j_**, const char ***_field_**,**
                                   **const void ****_data_**, size_t ***_length_**);**
    
           **int sd_journal_enumerate_data(sd_journal ***_j_**, const void ****_data_**,**
                                         **size_t ***_length_**);**
    
           **int sd_journal_enumerate_available_data(sd_journal ***_j_**,**
                                                   **const void ****_data_**,**
                                                   **size_t ***_length_**);**
    
           **void sd_journal_restart_data(sd_journal ***_j_**);**
    
           **SD_JOURNAL_FOREACH_DATA(sd_journal ***_j_**, const void ***_data_**,**
                                   **size_t** _length_**);**
    
           **int sd_journal_set_data_threshold(sd_journal ***_j_**, size_t** _sz_**);**
    
           **int sd_journal_get_data_threshold(sd_journal ***_j_**, size_t ***_sz_**);**
    


## DESCRIPTION



           **sd_journal_get_data()** gets the data object associated with a
           specific field from the current journal entry. It takes four
           arguments: the journal context object, a string with the field
           name to request, plus a pair of pointers to pointer/size variables
           where the data object and its size shall be stored in. The field
           name should be an entry field name. Well-known field names are
           listed in systemd.journal-fields(7), but any field can be
           specified. The returned data is in a read-only memory map and is
           only valid until the next invocation of **sd_journal_get_data()** ,
           **sd_journal_enumerate_data()** ,
           **sd_journal_enumerate_available_data()** , or when the read pointer is
           altered. Note that the data returned will be prefixed with the
           field name and "=". Also note that, by default, data fields larger
           than 64K might get truncated to 64K. This threshold may be changed
           and turned off with **sd_journal_set_data_threshold()**(see below).
    
           **sd_journal_enumerate_data()** may be used to iterate through all
           fields of the current entry. On each invocation the data for the
           next field is returned. The order of these fields is not defined.
           The data returned is in the same format as with
           **sd_journal_get_data()** and also follows the same life-time
           semantics.
    
           **sd_journal_enumerate_available_data()** is similar to
           **sd_journal_enumerate_data()** , but silently skips any fields which
           may be valid, but are too large or not supported by current
           implementation.
    
           **sd_journal_restart_data()** resets the data enumeration index to the
           beginning of the entry. The next invocation of
           **sd_journal_enumerate_data()** will return the first field of the
           entry again.
    
           Note that the **SD_JOURNAL_FOREACH_DATA()** macro may be used as a
           handy wrapper around **sd_journal_restart_data()** and
           **sd_journal_enumerate_available_data()**.
    
           Note that these functions will not work before sd_journal_next(3)
           (or related call) has been called at least once, in order to
           position the read pointer at a valid entry.
    
           **sd_journal_set_data_threshold()** may be used to change the data
           field size threshold for data returned by **sd_journal_get_data()** ,
           **sd_journal_enumerate_data()** and **sd_journal_enumerate_unique()**.
           This threshold is a hint only: it indicates that the client
           program is interested only in the initial parts of the data
           fields, up to the threshold in size — but the library might still
           return larger data objects. That means applications should not
           rely exclusively on this setting to limit the size of the data
           fields returned, but need to apply an explicit size limit on the
           returned data as well. This threshold defaults to 64K by default.
           To retrieve the complete data fields this threshold should be
           turned off by setting it to 0, so that the library always returns
           the complete data objects. It is recommended to set this threshold
           as low as possible since this relieves the library from having to
           decompress large compressed data objects in full.
    
           **sd_journal_get_data_threshold()** returns the currently configured
           data field size threshold.
    


## RETURN VALUE



           **sd_journal_get_data()** returns 0 on success or a negative
           errno-style error code.  **sd_journal_enumerate_data()** and
           **sd_journal_enumerate_available_data()** return a positive integer if
           the next field has been read, 0 when no more fields remain, or a
           negative errno-style error code.  **sd_journal_restart_data()** does
           not return anything.  **sd_journal_set_data_threshold()** and
           **sd_journal_get_threshold()** return 0 on success or a negative
           errno-style error code.
    
       **Errors**
           Returned errors may indicate the following problems:
    
           **-EINVAL**
               One of the required parameters is **NULL** or invalid.
    
               Added in version 246.
    
           **-ECHILD**
               The journal object was created in a different process, library
               or module instance.
    
               Added in version 246.
    
           **-EADDRNOTAVAIL**
               The read pointer is not positioned at a valid entry;
               sd_journal_next(3) or a related call has not been called at
               least once.
    
               Added in version 246.
    
           **-ENOENT**
               The current entry does not include the specified field.
    
               Added in version 246.
    
           **-ENOMEM**
               Memory allocation failed.
    
               Added in version 246.
    
           **-ENOBUFS**
               A compressed entry is too large.
    
               Added in version 246.
    
           **-E2BIG**
               The data field is too large for this computer architecture
               (e.g. above 4 GB on a 32-bit architecture).
    
               Added in version 246.
    
           **-EPROTONOSUPPORT**
               The journal is compressed with an unsupported method or the
               journal uses an unsupported feature.
    
               Added in version 246.
    
           **-EBADMSG**
               The journal is corrupted (possibly just the entry being
               iterated over).
    
               Added in version 246.
    
           **-EIO**
               An I/O error was reported by the kernel.
    
               Added in version 246.
    


## NOTES



           All functions listed here are thread-agnostic and only a single
           specific thread may operate on a given object during its entire
           lifetime. It is safe to allocate multiple independent objects and
           use each from a specific thread in parallel. However, it is not
           safe to allocate such an object in one thread, and operate or free
           it from any other, even if locking is used to ensure these threads
           do not operate on it at the very same time.
    
           Functions described here are available as a shared library, which
           can be compiled against and linked to with the
           **libsystemd pkg-config**(1) file.
    


## EXAMPLES



           See sd_journal_next(3) for a complete example how to use
           **sd_journal_get_data()**.
    
           Use the **SD_JOURNAL_FOREACH_DATA()** macro to iterate through all
           fields of the current journal entry:
    
               ...
               int print_fields(sd_journal *j) {
                 const void *data;
                 size_t length;
                 SD_JOURNAL_FOREACH_DATA(j, data, length)
                   printf("%.*s\n", (int) length, data);
               }
               ...
    


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