to provide more detail, again, starting logstash under systemd gives a fatal error also, though a different one.
this is the entire text of the log upon startup (it repeats over and over every minute or so)
[2022-09-01T20:22:44,697][INFO ][logstash.runner ] Log4j configuration path used is: /etc/logstash/log4j2.properties
[2022-09-01T20:22:44,717][INFO ][logstash.runner ] Starting Logstash {"logstash.version"=>"7.17.6", "jruby.version"=>"jruby 9.2.20.1 (2.5.8) 2021-11-30 2a2962fbd1 OpenJDK 64-Bit Server VM 11.0.16+8 on 11.0.16+8 +indy +jit [linux-x86_64]"}
[2022-09-01T20:22:44,722][INFO ][logstash.runner ] JVM bootstrap flags: [-Xms1g, -Xmx1g, -XX:+UseConcMarkSweepGC, -XX:CMSInitiatingOccupancyFraction=75, -XX:+UseCMSInitiatingOccupancyOnly, -Djava.awt.headless=true, -Dfile.encoding=UTF-8, -Djdk.io.File.enableADS=true, -Djruby.compile.invokedynamic=true, -Djruby.jit.threshold=0, -Djruby.regexp.interruptible=true, -XX:+HeapDumpOnOutOfMemoryError, -Djava.security.egd=file:/dev/urandom, -Dlog4j2.isThreadContextMapInheritable=true]
[2022-09-01T20:22:44,730][DEBUG][logstash.modules.scaffold] Found module {:module_name=>"netflow", :directory=>"/usr/share/logstash/modules/netflow/configuration"}
[2022-09-01T20:22:44,732][DEBUG][logstash.plugins.registry] Adding plugin to the registry {:name=>"netflow", :type=>:modules, :class=>#<LogStash::Modules::Scaffold:0x4898cd22 @directory="/usr/share/logstash/modules/netflow/configuration", @module_name="netflow", @kibana_version_parts=["6", "0", "0"]>}
[2022-09-01T20:22:44,734][DEBUG][logstash.modules.scaffold] Found module {:module_name=>"fb_apache", :directory=>"/usr/share/logstash/modules/fb_apache/configuration"}
[2022-09-01T20:22:44,734][DEBUG][logstash.plugins.registry] Adding plugin to the registry {:name=>"fb_apache", :type=>:modules, :class=>#<LogStash::Modules::Scaffold:0xd2eb3a0 @directory="/usr/share/logstash/modules/fb_apache/configuration", @module_name="fb_apache", @kibana_version_parts=["6", "0", "0"]>}
[2022-09-01T20:22:45,190][DEBUG][logstash.runner ] -------- Logstash Settings (* means modified) ---------
[2022-09-01T20:22:45,190][DEBUG][logstash.runner ] *node.name: "thoth" (default: "vps019")
[2022-09-01T20:22:45,190][DEBUG][logstash.runner ] *path.data: "/var/lib/logstash" (default: "/usr/share/logstash/data")
[2022-09-01T20:22:45,190][DEBUG][logstash.runner ] modules.cli: <Java::OrgLogstashUtil::ModulesSettingArray:1 []>
[2022-09-01T20:22:45,190][DEBUG][logstash.runner ] modules: []
[2022-09-01T20:22:45,190][DEBUG][logstash.runner ] modules_list: []
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] modules_variable_list: []
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] modules_setup: false
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] config.test_and_exit: false
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] *config.reload.automatic: true (default: false)
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] *config.reload.interval: #<Java::OrgLogstashUtil::TimeValue:0x343418b2> (default: #<Java::OrgLogstashUtil::TimeValue:0x1812086>)
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] config.support_escapes: false
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] config.field_reference.parser: "STRICT"
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] metric.collect: true
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] pipeline.id: "main"
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] pipeline.system: false
[2022-09-01T20:22:45,191][DEBUG][logstash.runner ] pipeline.workers: 2
[2022-09-01T20:22:45,192][DEBUG][logstash.runner ] *pipeline.batch.size: 1 (default: 125)
[2022-09-01T20:22:45,192][DEBUG][logstash.runner ] pipeline.batch.delay: 50
[2022-09-01T20:22:45,200][DEBUG][logstash.runner ] pipeline.unsafe_shutdown: false
[2022-09-01T20:22:45,201][DEBUG][logstash.runner ] pipeline.java_execution: true
[2022-09-01T20:22:45,201][DEBUG][logstash.runner ] pipeline.reloadable: true
[2022-09-01T20:22:45,201][DEBUG][logstash.runner ] pipeline.plugin_classloaders: false
[2022-09-01T20:22:45,202][DEBUG][logstash.runner ] pipeline.separate_logs: false
[2022-09-01T20:22:45,202][DEBUG][logstash.runner ] pipeline.ordered: "auto"
[2022-09-01T20:22:45,204][DEBUG][logstash.runner ] pipeline.ecs_compatibility: "disabled"
[2022-09-01T20:22:45,205][DEBUG][logstash.runner ] path.plugins: []
[2022-09-01T20:22:45,208][DEBUG][logstash.runner ] *config.debug: true (default: false)
[2022-09-01T20:22:45,209][DEBUG][logstash.runner ] *log.level: "debug" (default: "info")
[2022-09-01T20:22:45,209][DEBUG][logstash.runner ] version: false
[2022-09-01T20:22:45,209][DEBUG][logstash.runner ] help: false
[2022-09-01T20:22:45,209][DEBUG][logstash.runner ] enable-local-plugin-development: false
[2022-09-01T20:22:45,210][DEBUG][logstash.runner ] log.format: "plain"
[2022-09-01T20:22:45,210][DEBUG][logstash.runner ] api.enabled: true
[2022-09-01T20:22:45,210][DEBUG][logstash.runner ] *api.http.host: "127.0.0.1" (via deprecated `http.host`; default: "127.0.0.1")
[2022-09-01T20:22:45,211][DEBUG][logstash.runner ] *http.host: "127.0.0.1"
[2022-09-01T20:22:45,211][DEBUG][logstash.runner ] *api.http.port: 9600..9700 (via deprecated `http.port`; default: 9600..9700)
[2022-09-01T20:22:45,211][DEBUG][logstash.runner ] *http.port: 9600..9700
[2022-09-01T20:22:45,211][DEBUG][logstash.runner ] api.environment: "production"
[2022-09-01T20:22:45,212][DEBUG][logstash.runner ] api.auth.type: "none"
[2022-09-01T20:22:45,212][DEBUG][logstash.runner ] api.ssl.enabled: false
[2022-09-01T20:22:45,212][DEBUG][logstash.runner ] queue.type: "memory"
[2022-09-01T20:22:45,213][DEBUG][logstash.runner ] queue.drain: false
[2022-09-01T20:22:45,213][DEBUG][logstash.runner ] queue.page_capacity: 67108864
[2022-09-01T20:22:45,216][DEBUG][logstash.runner ] queue.max_bytes: 1073741824
[2022-09-01T20:22:45,217][DEBUG][logstash.runner ] queue.max_events: 0
[2022-09-01T20:22:45,217][DEBUG][logstash.runner ] queue.checkpoint.acks: 1024
[2022-09-01T20:22:45,217][DEBUG][logstash.runner ] queue.checkpoint.writes: 1024
[2022-09-01T20:22:45,217][DEBUG][logstash.runner ] queue.checkpoint.interval: 1000
[2022-09-01T20:22:45,218][DEBUG][logstash.runner ] queue.checkpoint.retry: true
[2022-09-01T20:22:45,218][DEBUG][logstash.runner ] dead_letter_queue.enable: false
[2022-09-01T20:22:45,224][DEBUG][logstash.runner ] dead_letter_queue.max_bytes: 1073741824
[2022-09-01T20:22:45,224][DEBUG][logstash.runner ] dead_letter_queue.flush_interval: 5000
[2022-09-01T20:22:45,225][DEBUG][logstash.runner ] slowlog.threshold.warn: #<Java::OrgLogstashUtil::TimeValue:0x43b60ce1>
[2022-09-01T20:22:45,225][DEBUG][logstash.runner ] slowlog.threshold.info: #<Java::OrgLogstashUtil::TimeValue:0x4e260e04>
[2022-09-01T20:22:45,225][DEBUG][logstash.runner ] slowlog.threshold.debug: #<Java::OrgLogstashUtil::TimeValue:0x4f3b5c60>
[2022-09-01T20:22:45,225][DEBUG][logstash.runner ] slowlog.threshold.trace: #<Java::OrgLogstashUtil::TimeValue:0x5d947961>
[2022-09-01T20:22:45,226][DEBUG][logstash.runner ] keystore.classname: "org.logstash.secret.store.backend.JavaKeyStore"
[2022-09-01T20:22:45,226][DEBUG][logstash.runner ] *keystore.file: "/etc/logstash/logstash.keystore" (default: "/usr/share/logstash/config/logstash.keystore")
[2022-09-01T20:22:45,226][DEBUG][logstash.runner ] *path.queue: "/var/lib/logstash/queue" (default: "/usr/share/logstash/data/queue")
[2022-09-01T20:22:45,226][DEBUG][logstash.runner ] *path.dead_letter_queue: "/var/lib/logstash/dead_letter_queue" (default: "/usr/share/logstash/data/dead_letter_queue")
[2022-09-01T20:22:45,227][DEBUG][logstash.runner ] *path.settings: "/etc/logstash" (default: "/usr/share/logstash/config")
[2022-09-01T20:22:45,227][DEBUG][logstash.runner ] *path.logs: "/var/log/logstash" (default: "/usr/share/logstash/logs")
[2022-09-01T20:22:45,227][DEBUG][logstash.runner ] xpack.monitoring.enabled: false
[2022-09-01T20:22:45,227][DEBUG][logstash.runner ] xpack.monitoring.elasticsearch.hosts: ["http://localhost:9200"]
[2022-09-01T20:22:45,228][DEBUG][logstash.runner ] xpack.monitoring.collection.interval: #<Java::OrgLogstashUtil::TimeValue:0x7b16d337>
[2022-09-01T20:22:45,228][DEBUG][logstash.runner ] xpack.monitoring.collection.timeout_interval: #<Java::OrgLogstashUtil::TimeValue:0x4155a965>
[2022-09-01T20:22:45,228][DEBUG][logstash.runner ] xpack.monitoring.elasticsearch.username: "logstash_system"
[2022-09-01T20:22:45,228][DEBUG][logstash.runner ] xpack.monitoring.elasticsearch.ssl.verification_mode: "certificate"
[2022-09-01T20:22:45,229][DEBUG][logstash.runner ] xpack.monitoring.elasticsearch.sniffing: false
[2022-09-01T20:22:45,229][DEBUG][logstash.runner ] xpack.monitoring.collection.pipeline.details.enabled: true
[2022-09-01T20:22:45,229][DEBUG][logstash.runner ] xpack.monitoring.collection.config.enabled: true
[2022-09-01T20:22:45,229][DEBUG][logstash.runner ] monitoring.enabled: false
[2022-09-01T20:22:45,230][DEBUG][logstash.runner ] monitoring.elasticsearch.hosts: ["http://localhost:9200"]
[2022-09-01T20:22:45,230][DEBUG][logstash.runner ] monitoring.collection.interval: #<Java::OrgLogstashUtil::TimeValue:0xb52d046>
[2022-09-01T20:22:45,231][DEBUG][logstash.runner ] monitoring.collection.timeout_interval: #<Java::OrgLogstashUtil::TimeValue:0x65bc66bb>
[2022-09-01T20:22:45,231][DEBUG][logstash.runner ] monitoring.elasticsearch.username: "logstash_system"
[2022-09-01T20:22:45,231][DEBUG][logstash.runner ] monitoring.elasticsearch.ssl.verification_mode: "certificate"
[2022-09-01T20:22:45,232][DEBUG][logstash.runner ] monitoring.elasticsearch.sniffing: false
[2022-09-01T20:22:45,233][DEBUG][logstash.runner ] monitoring.collection.pipeline.details.enabled: true
[2022-09-01T20:22:45,233][DEBUG][logstash.runner ] monitoring.collection.config.enabled: true
[2022-09-01T20:22:45,233][DEBUG][logstash.runner ] node.uuid: ""
[2022-09-01T20:22:45,234][DEBUG][logstash.runner ] xpack.management.enabled: false
[2022-09-01T20:22:45,234][DEBUG][logstash.runner ] xpack.management.logstash.poll_interval: #<Java::OrgLogstashUtil::TimeValue:0x202b765f>
[2022-09-01T20:22:45,234][DEBUG][logstash.runner ] xpack.management.pipeline.id: ["main"]
[2022-09-01T20:22:45,234][DEBUG][logstash.runner ] xpack.management.elasticsearch.username: "logstash_system"
[2022-09-01T20:22:45,235][DEBUG][logstash.runner ] xpack.management.elasticsearch.hosts: ["https://localhost:9200"]
[2022-09-01T20:22:45,235][DEBUG][logstash.runner ] xpack.management.elasticsearch.ssl.verification_mode: "certificate"
[2022-09-01T20:22:45,236][DEBUG][logstash.runner ] xpack.management.elasticsearch.sniffing: false
[2022-09-01T20:22:45,236][DEBUG][logstash.runner ] --------------- Logstash Settings -------------------
[2022-09-01T20:22:45,279][DEBUG][logstash.config.source.multilocal] Reading pipeline configurations from YAML {:location=>"/etc/logstash/pipelines.yml"}
[2022-09-01T20:22:45,313][FATAL][org.logstash.Logstash ] Logstash stopped processing because of an error: (SystemExit) exit
org.jruby.exceptions.SystemExit: (SystemExit) exit
at org.jruby.RubyKernel.exit(org/jruby/RubyKernel.java:747) ~[jruby-complete-9.2.20.1.jar:?]
at org.jruby.RubyKernel.exit(org/jruby/RubyKernel.java:710) ~[jruby-complete-9.2.20.1.jar:?]
Our installation is not new, btw. it's been running, in production, for over a year now.