[HDFS-13397] start-dfs.sh and hdfs --daemon start datanode say "ERROR: Cannot set priority of datanode process XXXX"

• Type: New Feature
• Status: Resolved
• Priority: Major
• Resolution: Invalid
• Affects Version/s: 3.0.1
• Component/s: hdfs
• Release Note: This fix apparently does not work in all cases, will withdraw and re-post after further investigation
• Assignee: Unassigned
• Reporter: Jeff Hubbs
• Created: 04/Apr/18 19:01
• Updated: 04/Apr/18 19:36
• Resolved: 04/Apr/18 19:36

Description

When executing

$HADOOP_HOME/bin/hdfs --daemon start datanode

as a regular user (e.g. "hdfs") you achieve fail saying

ERROR: Cannot set priority of datanode process XXXX

where XXXX is some PID.

It turned out that this is because at least on Gentoo Linux (and I think this is pretty well universal), by default a regular user process can't increase the priority of itself or any of the user's other processes. To fix this, I added these lines to /etc/security/limits.conf [NOTE: the users hdfs, yarn, and mapred are in the group called hadoop on this system]:

@hadoop        hard    nice            -15
@hadoop        hard    priority        -15

This change will need to be made on all datanodes.

The need to enable [at minimum] the hdfs user to raise its processes' priority needs to be added to the documentation. This is not a problem I observed under 3.0.0.