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
1024Check 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>/limitsreplacing <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 filesValidate 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.
| OS | SysVinit(deprecated) | systemd |
|---|---|---|
RedHat Enterprise Linux >=7, CentOS >=7, fedora >=16 |
no |
yes |
RedHat Enterprise Linux ⇐6, CentOS ⇐6, fedora ⇐15 |
yes |
no |
Ubuntu >=16.04, Debian >=8 |
no |
yes |
If your system is using systemd
neo4j is running as a service
run the following command
> sudo systemctl edit neo4j.serviceand append the following
[Service]
LimitNOFILE=60000Follow the product documentation
neo4j is as a normal process
run the following command
> $ sudo vi /etc/systemd/system.confand uncomment and define DefaultLimitNOFILE
[Manager]
...
DefaultLimitNOFILE=60000run the following command
> $ sudo vi /etc/systemd/user.confand uncomment and define LimitNOFILE
[Manager]
#...
DefaultLimitNOFILE=60000If 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 pam_limits.so-
/etc/pam.d/common-session-noninteractive also needs to have this line in it:
session required pam_limits.soKeep 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.
Related issue: NativeFSLock strange behavior - Lock obtain timed out
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.
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