pespin has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-gsm-manuals/+/41844?usp=email )
Change subject: logging: Improve systemd-journal log documentation ......................................................................
logging: Improve systemd-journal log documentation
Change-Id: I9a67b9b8c38868004a794164724cdffc5b86a044 --- M common/chapters/logging.adoc 1 file changed, 18 insertions(+), 0 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-gsm-manuals refs/changes/44/41844/1
diff --git a/common/chapters/logging.adoc b/common/chapters/logging.adoc index 57ffbae..1fa16af 100644 --- a/common/chapters/logging.adoc +++ b/common/chapters/logging.adoc @@ -439,6 +439,24 @@ being passed to systemd. No additional fields will be attached, except the logging level (`PRIORITY`). This mode is similar to _syslog_ and _stderr_.
+NOTE: systmed-journal logging target uses libsystemd, which implements _Native +Journal Protocol_ (_AF_UNIX _DATAGRAM_ socket). That socket is internally +configured in synchronous blocking I/O mode, which means transmitting a big +amount of messages or text over it in a short amount of time (before +systemd-journald has time to read it) could potentially block the osmocom +program's thread issuing the logging. libsystemd currently sets the _AF_UNIX_ +socket `SO_SNDBUF` to 8MB, In Linux, the `SO_SNDBUF` value being set on the +socket will be trimmed by the kernel to a maximum allowed by sysctl +`net.core.wmem_max`. Hence, if you want to be on a safer side minimizing +dropping messages or blocking the process (depending on the I/O mode set), make +sure sysctl `net.core.wmem_max` on your system is set to `4194304` (8MB) or +more. Moreover, limits amount of messages queued in _AF_UNIX_ sockets to value +from sysctl `net.unix.max_dgram_qlen`, so you may also want to increase that one +to be on the safe side if planning to log with a high frequency. + +NOTE: Linux Kernel used to have a `net.core.wmem_max` of `212992`(208KB) until +recently (2025, a6d4f25888b83b8300aef28d9ee22765c1cc9b34), where it was +increased to `4194304` (4MB) .
==== Logging to stderr