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-Xlog Usage: -Xlog[:[selections][:[output][:[decorators][:output-options]]]]
where 'selections' are combinations of tags and levels of the form tag1[+tag2...][*][=level][,...]
NOTE: Unless wildcard (*) is specified, only log messages tagged with exactly the tags specified will be matched.
Available log levels:
off, trace, debug, info, warning, error
Available log decorators:
time (t), utctime (utc), uptime (u), timemillis (tm), uptimemillis (um), timenanos (tn), uptimenanos (un), hostname (hn), pid (p), tid (ti), level (l), tags (tg)
Decorators can also be specified as 'none' for no decoration.
Available log tags:
add, age, alloc, annotation, arguments, attach, barrier, blocks, bot, breakpoint, bytecode, cds, census, class, classhisto, cleanup, codecache, compaction, compilation, condy, constantpool, constraints, container, continuations, coops, cpu, cset, data, datacreation, dcmd, decoder, defaultmethods, director, dump, dynamic, ergo, event, exceptions, exit, finalizer, fingerprint, free, freelist, gc, handshake, hashtables, heap, humongous, ihop, iklass, indy, init, inlining, install, interpreter, itables, jfr, jit, jni, jvmci, jvmti, lambda, library, liveness, load, loader, logging, malloc, map, mark, marking, membername, memops, metadata, metaspace, methodcomparator, methodhandles, mirror, mmu, module, monitorinflation, monitormismatch, nestmates, nmethod, nmt, normalize, numa, objecttagging, obsolete, oldobject, oom, oopmap, oops, oopstorage, os, owner, pagesize, parser, patch, path, perf, periodic, phases, plab, placeholders, preempt, preorder, preview, promotion, protectiondomain, ptrqueue, purge, record, redefine, ref, refine, region, reloc, remset, resolve, safepoint, sampling, scavenge, sealed, setting, smr, stackbarrier, stackmap, stacktrace, stackwalk, start, startup, startuptime, state, stats, streaming, stringdedup, stringtable, subclass, survivor, suspend, sweep, symboltable, system, table, task, thread, throttle, timer, tlab, tracking, unload, unshareable, update, valuebasedclasses, verification, verify, vmmutex, vmoperation, vmthread, vtables, vtablestubs
Specifying 'all' instead of a tag combination matches all tag combinations.
Described tag sets:
logging: Logging for the log framework itself
Available log outputs:
stdout/stderr
file=<filename>
If the filename contains %p and/or %t, they will expand to the JVM's PID and startup timestamp, respectively.
Available log output options:
foldmultilines=.. - If set to true, a log event that consists of multiple lines will be folded into a single line by replacing newline characters with the sequence '\' and 'n' in the output. Existing single backslash characters will also be replaced with a sequence of two backslashes so that the conversion can be reversed. This option is safe to use with UTF-8 character encodings, but other encodings may not work.
Additional file output options:
filesize=.. - Target byte size for log rotation (supports K/M/G suffix). If set to 0, log rotation will not trigger automatically, but can be performed manually (see the VM.log DCMD).
filecount=.. - Number of files to keep in rotation (not counting the active file). If set to 0, log rotation is disabled. This will cause existing log files to be overwritten.
Asynchronous logging (off by default):
-Xlog:async
All log messages are written to an intermediate buffer first and will then be flushed to the corresponding log outputs by a standalone thread. Write operations at logsites are guaranteed non-blocking.
Some examples:
-Xlog
Log all messages up to 'info' level to stdout with 'uptime', 'levels' and 'tags' decorations.
(Equivalent to -Xlog:all=info:stdout:uptime,levels,tags).
-Xlog:gc
Log messages tagged with 'gc' tag up to 'info' level to stdout, with default decorations.
-Xlog:gc,safepoint
Log messages tagged either with 'gc' or 'safepoint' tags, both up to 'info' level, to stdout, with default decorations.
(Messages tagged with both 'gc' and 'safepoint' will not be logged.)
-Xlog:gc+ref=debug
Log messages tagged with both 'gc' and 'ref' tags, up to 'debug' level, to stdout, with default decorations.
(Messages tagged only with one of the two tags will not be logged.)
-Xlog:gc=debug:file=gc.txt:none
Log messages tagged with 'gc' tag up to 'debug' level to file 'gc.txt' with no decorations.
-Xlog:gc=trace:file=gctrace.txt:uptimemillis,pid:filecount=5,filesize=1m
Log messages tagged with 'gc' tag up to 'trace' level to a rotating fileset of 5 files of size 1MB,
using the base name 'gctrace.txt', with 'uptimemillis' and 'pid' decorations.
-Xlog:gc::uptime,tid
Log messages tagged with 'gc' tag up to 'info' level to output 'stdout', using 'uptime' and 'tid' decorations.
-Xlog:gc*=info,safepoint*=off
Log messages tagged with at least 'gc' up to 'info' level, but turn off logging of messages tagged with 'safepoint'.
(Messages tagged with both 'gc' and 'safepoint' will not be logged.)
-Xlog:disable -Xlog:safepoint=trace:safepointtrace.txt
Turn off all logging, including warnings and errors,
and then enable messages tagged with 'safepoint' up to 'trace' level to file 'safepointtrace.txt'.
-Xlog:async -Xlog:gc=debug:file=gc.log -Xlog:safepoint=trace
Write logs asynchronously. Enable messages tagged with 'safepoint' up to 'trace' level to stdout
and messages tagged with 'gc' up to 'debug' level to file 'gc.log'.
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