Could fluent bit be able to upgrade from 3.2.7 to 4.0.0?

[hahakiki2010]

Could fluent bit be able to upgrade from 3.2.7 to 4.0.0? I checked the upgrade notes of 4.0.0 below, but only info are found for 1.9.x previous
https://docs.fluentbit.io/manual/installation/upgrade-notes

[patrick-stephens]

Yes

[mahesh-hemke]

Is there any document to upgrade the fluent bit from 3.2 to 4.2 ? I could not see any document in official page , I also tried to upgrade it to 4.2 from 3.2 but getting error as fluent bit service is not stable it is continuously restarting in few seconds.

JFYI, For upgrade I just upgrade the fluent bit package nothing else

then I downgraded it to 3.2 then it working fine.

https://docs.fluentbit.io/manual/4.2/installation/upgrade_notes

[mahesh-hemke]

fluent bit service is crashing and getting below errors, with the same configuration it is working perfectly on 3.2 version

fluent-bit[1131245]: Fluent Bit v4.2 – Direct Routes Ahead
fluent-bit[1131245]: Celebrating 10 Years of Open, Fluent Innovation!
fluent-bit[1131245]: [2025/12/15 09:48:32] [engine] caught signal (SIGSEGV)
fluent-bit[1131245]: #0 0x73db9a8ee2a1 in ???() at ???:0
fluent-bit[1131245]: #1 0x73db9ae0aa26 in ???() at ???:0
fluent-bit[1131245]: #2 0x73db9ae5af9a in ???() at ???:0
fluent-bit[1131245]: #3 0x73db9ae4c5f2 in ???() at ???:0
fluent-bit[1131245]: #4 0x572ac0704564 in tls_net_handshake() at src/tls/openssl.c:1399
fluent-bit[1131245]: #5 0x572ac0705204 in flb_tls_session_create() at src/tls/flb_tls.c:630
fluent-bit[1131245]: #6 0x572ac0717ac4 in flb_io_net_accept() at src/flb_io.c:91
fluent-bit[1131245]: #7 0x572ac06e1542 in flb_downstream_conn_get() at src/flb_downstream.c:340
fluent-bit[1131245]: #8 0x572ac07a2aad in in_fw_collect() at plugins/in_forward/fw.c:133
fluent-bit[1131245]: #9 0x572ac06be08a in input_collector_fd() at src/flb_input_thread.c:166
fluent-bit[1131245]: #10 0x572ac06be08a in engine_handle_event() at src/flb_input_thread.c:181
fluent-bit[1131245]: #11 0x572ac06be08a in input_thread() at src/flb_input_thread.c:420
fluent-bit[1131245]: #12 0x572ac06e6f81 in step_callback() at src/flb_worker.c:43
fluent-bit[1131245]: #13 0x73db9a09caa3 in ???() at ???:0
fluent-bit[1131245]: #14 0x73db9a129c6b in ???() at ???:0
fluent-bit[1131245]: #15 0xffffffffffffffff in ???() at ???:0
systemd[1]: fluent-bit.service: Main process exited, code=dumped, status=6/ABRT
systemd[1]: fluent-bit.service: Failed with result 'core-dump'.
systemd[1]: fluent-bit.service: Consumed 2.091s CPU time.

fluent-bit[1131594]: Fluent Bit v4.2 – Direct Routes Ahead
fluent-bit[1131594]: Celebrating 10 Years of Open, Fluent Innovation!
fluent-bit[1131594]: [2025/12/15 09:48:44] [engine] caught signal (SIGSEGV)
fluent-bit[1131594]: #0 0x64e1e2ebbde3 in arena_dalloc_large() at lib/jemalloc-5.3.0/include/jemalloc/internal/arena_inlines_b.h:297
fluent-bit[1131594]: #1 0x64e1e2ebbde3 in arena_dalloc() at lib/jemalloc-5.3.0/include/jemalloc/internal/arena_inlines_b.h:334
fluent-bit[1131594]: #2 0x64e1e2ebbde3 in idalloctm() at lib/jemalloc-5.3.0/include/jemalloc/internal/jemalloc_internal_inlines_c.h:120
fluent-bit[1131594]: #3 0x64e1e2ebbde3 in ifree() at lib/jemalloc-5.3.0/src/jemalloc.c:2887
fluent-bit[1131594]: #4 0x64e1e2ebbde3 in je_free_default() at lib/jemalloc-5.3.0/src/jemalloc.c:3014
fluent-bit[1131594]: #5 0x64e1e2f8a975 in flb_free() at include/fluent-bit/flb_mem.h:127
fluent-bit[1131594]: #6 0x64e1e2f8a975 in flb_log_event_encoder_dynamic_field_scope_leave() at src/flb_log_event_encoder_dynamic_field.c:109
fluent-bit[1131594]: #7 0x64e1e2f8abe9 in flb_log_event_encoder_dynamic_field_flush_scopes() at src/flb_log_event_encoder_dynamic_field.c:210
fluent-bit[1131594]: #8 0x64e1e2f8abe9 in flb_log_event_encoder_dynamic_field_reset() at src/flb_log_event_encoder_dynamic_field.c:240
fluent-bit[1131594]: #9 0x64e1e30457aa in flb_log_event_encoder_set_metadata_from_msgpack_object() at include/fluent-bit/flb_log_event_encoder_metadata_macros.h:135
fluent-bit[1131594]: #10 0x64e1e30457aa in fw_process_forward_mode_entry() at plugins/in_forward/fw_prot.c:973
fluent-bit[1131594]: #11 0x64e1e30457aa in fw_prot_process() at plugins/in_forward/fw_prot.c:1443
fluent-bit[1131594]: #12 0x64e1e3041ba6 in fw_conn_event() at plugins/in_forward/fw_conn.c:108
fluent-bit[1131594]: #13 0x64e1e2f5c0be in input_thread() at src/flb_input_thread.c:447
fluent-bit[1131594]: #14 0x64e1e2f84f81 in step_callback() at src/flb_worker.c:43
fluent-bit[1131594]: #15 0x73650509caa3 in ???() at ???:0
fluent-bit[1131594]: #16 0x736505129c6b in ???() at ???:0
fluent-bit[1131594]: #17 0xffffffffffffffff in ???() at ???:0
systemd[1]: fluent-bit.service: Main process exited, code=dumped, status=6/ABRT
systemd[1]: fluent-bit.service: Failed with result 'core-dump'.
systemd[1]: fluent-bit.service: Consumed 2.458s CPU time.

fluent-bit[1131943]: Fluent Bit v4.2 – Direct Routes Ahead
fluent-bit[1131943]: Celebrating 10 Years of Open, Fluent Innovation!
fluent-bit[1131943]: [2025/12/15 09:48:54] [engine] caught signal (SIGSEGV)
fluent-bit[1131943]: [2025/12/15 09:48:54] [engine] caught signal (SIGSEGV)
fluent-bit[1131943]: #0 0x61bfd7f1cde3 in arena_dalloc_large() at lib/jemalloc-5.3.0/include/jemalloc/internal/arena_inlines_b.h:297
fluent-bit[1131943]: #1 0x61bfd7f1cde3 in arena_dalloc() at lib/jemalloc-5.3.0/include/jemalloc/internal/arena_inlines_b.h:334
fluent-bit[1131943]: #2 0x61bfd7f1cde3 in idalloctm() at lib/jemalloc-5.3.0/include/jemalloc/internal/jemalloc_internal_inlines_c.h:120
fluent-bit[1131943]: #3 0x61bfd7f1cde3 in ifree() at lib/jemalloc-5.3.0/src/jemalloc.c:2887
fluent-bit[1131943]: #4 0x61bfd7f1cde3 in je_free_default() at lib/jemalloc-5.3.0/src/jemalloc.c:3014
fluent-bit[1131943]: #5 0x61bfd7fe92cb in msgpack_unpacked_destroy() at lib/msgpack-c/include/msgpack/unpack.h:260
fluent-bit[1131943]: #6 0x61bfd7fe92cb in flb_log_event_decoder_destroy() at src/flb_log_event_decoder.c:158
fluent-bit[1131943]: #7 0x61bfd8175204 in cb_rewrite_tag_filter() at plugins/filter_rewrite_tag/rewrite_tag.c:552
fluent-bit[1131943]: #8 0x61bfd7fbdf23 in flb_filter_do() at src/flb_filter.c:202
fluent-bit[1131943]: #9 0x61bfd7fbabf9 in input_chunk_append_raw() at src/flb_input_chunk.c:2775
fluent-bit[1131943]: #10 0x61bfd7fbb5ba in flb_input_chunk_ring_buffer_collector() at src/flb_input_chunk.c:3085
fluent-bit[1131943]: #11 0x61bfd7fd6b8f in flb_engine_start() at src/flb_engine.c:1275
fluent-bit[1131943]: #12 0x61bfd7fa9727 in flb_lib_worker() at src/flb_lib.c:904
fluent-bit[1131943]: #13 0x73dad5a9caa3 in ???() at ???:0
fluent-bit[1131943]: #14 0x73dad5b29c6b in ???() at ???:0
fluent-bit[1131943]: #15 0xffffffffffffffff in ???() at ???:0
systemd[1]: fluent-bit.service: Main process exited, code=dumped, status=6/ABRT
systemd[1]: fluent-bit.service: Failed with result 'core-dump'.
systemd[1]: fluent-bit.service: Consumed 1.589s CPU time.

[patrick-stephens]

You raised this in Slack as well but there are no details here of what config you are using or what target you are upgrading or even if you used official packages or compiled from source?

[patrick-stephens]

https://docs.fluentbit.io/manual/installation/upgrade-notes as per the other response in Slack - you can also search in the docs

[mahesh-hemke]

I have provided the config details in slack , I have used the official package