Elastic search not starting

Graylog Central (peer support)
1 
Starting elasticsearch: Exception in thread "main" java.lang.IllegalStateException: Failed to created node environment
Likely root cause: java.nio.file.AccessDeniedException: /var/lib/elasticsearch/graylog/nodes/1
	at sun.nio.fs.UnixException.translateToIOException(UnixException.java:84)
	at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:102)
	at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:107)
	at sun.nio.fs.UnixFileSystemProvider.createDirectory(UnixFileSystemProvider.java:384)
	at java.nio.file.Files.createDirectory(Files.java:674)
	at java.nio.file.Files.createAndCheckIsDirectory(Files.java:781)
	at java.nio.file.Files.createDirectories(Files.java:767)
	at org.elasticsearch.env.NodeEnvironment.<init>(NodeEnvironment.java:169)
	at org.elasticsearch.node.Node.<init>(Node.java:165)
	at org.elasticsearch.node.Node.<init>(Node.java:140)
	at org.elasticsearch.node.NodeBuilder.build(NodeBuilder.java:143)
	at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:194)
	at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:286)
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:45)
Refer to the log for complete error details.
2

Make sure that Elasticsearch (or more specifically: the system user running the Elasticsearch process) is able to write into the /var/lib/elasticsearch directory and all its subdirectories.