Knowledge Base

Number of open files

GNU/Linux and Mac OS operating systems impose an upper limit on the number of concurrent files a user may have open.

This article covers how to configure the number of open files on GNU/Linux that use systemd or sysvinitd.

For Mac OS, please check the following article: Setting Max Open File Limits on Mac OSX

Check the settings for current user and current session

This number is reported for the current user and session with the ulimit -n command:

user@localhost:~$ ulimit -n

Check the setting for a running process

To monitor how many open files a user has, you can run:

> lsof -u <user>

replacing <user> with the linux username who started the Neo4j process.

To understand the limits for one specific ProcessID one can also run:

> cat /proc/<processID>/limits

replacing <processID> with the linux processID for the running Neo4j process.

This will produce output similar to

$ cat /proc/5219/limits
Limit                     Soft Limit           Hard Limit           Units
Max cpu time              unlimited            unlimited            seconds
Max file size             unlimited            unlimited            bytes
Max data size             unlimited            unlimited            bytes
Max stack size            8388608              unlimited            bytes
Max core file size        0                    unlimited            bytes
Max resident set          unlimited            unlimited            bytes
Max processes             31357                31357                processes
Max open files            40000                40000                files

Validate the correct settings

Neo4j will report the current setting for number of file descriptors in the debug.log as following:

2019-01-02 13:39:27.003+0000 INFO [o.n.i.d.DiagnosticsManager] Max number of file descriptors: 10000

The usual default is 1024 and is often not enough. We recommend setting this to 40000 to ensure Neo4j works correctly.

It is possible to set the limit with the ulimit -n command, but only for the root user, and it only affects the current session, so it’s not permanent. Also, it will not affect your processes that are already running.

It is necessary to check this before and after changing the file descriptor limit.

Change file descriptor limit

Depending on the System and Service Manager, the configuration steps differ. Since 2015, the majority of Linux distributions have adopted systemd and it is considered a de facto standard.

Table 1. Table Systemd vs SysVinit usage as of 2019
OS SysVinit(deprecated) systemd

RedHat Enterprise Linux >=7, CentOS >=7, fedora >=16



RedHat Enterprise Linux ⇐6, CentOS ⇐6, fedora ⇐15



Ubuntu >=16.04, Debian >=8



If your system is using systemd

neo4j is running as a service

run the following command

> sudo systemctl edit neo4j.service

and append the following


neo4j is as a normal process

run the following command

> $ sudo vi /etc/systemd/system.conf

and uncomment and define DefaultLimitNOFILE


run the following command

> $ sudo vi /etc/systemd/user.conf

and uncomment and define LimitNOFILE


If your system is using SysVinit

The actual way to raise your file limits consists of editing three files:

  • /etc/security/limits.conf needs to have these lines in it:

neo4j  soft  nofile  40000
neo4j  hard  nofile  40000
  • /etc/pam.d/common-session needs to have this line in it:

session required
  • /etc/pam.d/common-session-noninteractive also needs to have this line in it:

session required

Keep in mind that limits can be easily modified by anything responsible for execution of your processes. If running ulimit -n (with the correct user) is giving you the number you just set, but cat /proc/{process_id}/limits is still printing the low number, you almost certainly have a process manager, an init script, or something similar overriding your limits. One last thing worth noting is that processes inherit the limits of the parent process.

Sometimes you’ll see the following error in the logs: LockObtainFailedException: Lock obtain timed out: NativeFSLock

In this case you might want to increase the number of file descriptors to an even higher value.

For example: if you encounter the issue with 40000, try to increase it to 80000 or higher.