# Weird error: \`SystemError: memory mapping failed: Too many open files in system\`
**URL:** https://discourse.julialang.org/t/weird-error-systemerror-memory-mapping-failed-too-many-open-files-in-system/41944
**Category:** General Usage
**Created:** [June 23, 2020, 3:25pm UTC](https://discourse.julialang.org/t/weird-error-systemerror-memory-mapping-failed-too-many-open-files-in-system/41944 "2020-06-23T15:25:15Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@affans](https://discourse.julialang.org/u/affans)
#### Post date: [June 23, 2020, 3:25pm UTC](https://discourse.julialang.org/t/weird-error-systemerror-memory-mapping-failed-too-many-open-files-in-system/41944/1 "2020-06-23T15:25:15Z")
I am trying to run something in parallel. Suppose I have the following module loaded and that I am using `ClusterManagers.jl` to connect to a cluster.
```julia
@everywhere module ldf
using some packages...
function read_df()
validstates = ("...")
#create a return vector
df_of_states = Array{DataFrame, 1}(undef, 50)
for (i, vs) in enumerate(validstates)
df_of_states[i] = CSV.File(fn, header=false) |> DataFrame
end
return df_of_states
end
export read_df
const dfs = read_df()
export dfs
end
```
The line `const dfs = read_df()` makes it so that when the `@everywhere` is run on all the workers, the csv files are read and stored in a `const` variable. I want to make use these dataframes in other functions. The size of each dataframes is `20000 x 141`.
So now suppose on node001 where there are 32 workers launched, each worker with a separate copy of `ldf`, each creating a variable called `dfs` and reading those files… I get the following error
```julia
On worker 2:
│ SystemError: memory mapping failed: Too many open files in system
│ #systemerror#51 at ./error.jl:168
│ #systemerror#50 at ./error.jl:167 [inlined]
│ systemerror at ./error.jl:167 [inlined]
│ #mmap#1 at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.4/Mmap/src/Mmap.jl:209
│ #mmap#14 at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.4/Mmap/src/Mmap.jl:251 [inlined]
│ mmap at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.4/Mmap/src/Mmap.jl:251 [inlined]
│ parsetape at /home/affans/.julia/packages/CSV/vyG0T/src/file.jl:474
│ #File#28 at /home/affans/.julia/packages/CSV/vyG0T/src/file.jl:252
│ read_df at /home/affans/lancetid_actualinfection_post.jl:33
│ top-level scope at /home/affans/lancetid_actualinfection_post.jl:39
│ eval at ./boot.jl:331
```
It’s a fairly obvious error… I am opening up too many files, but I was wondering what the root cause of this is? It’s not out of memory error (as each worker has almost 4gb of RAM to work with, with a total of 128gb).
The solution for me here is to move the `read_df()` back to the head node and just pass to the workers the relevant data… but just wanted to get some insight on this.
---
### Author:  [@pixel27](https://discourse.julialang.org/u/pixel27)
#### Post date: [June 23, 2020, 3:48pm UTC](https://discourse.julialang.org/t/weird-error-systemerror-memory-mapping-failed-too-many-open-files-in-system/41944/2 "2020-06-23T15:48:27Z")
I’m assuming you are on linux. You might want to check `/proc/sys/fs/file-max`. That should be the maximum number of file descriptors can be open (in the system) at once. (On my system that is 9223372036854775807 but maybe it’s smaller on yours.)
You should also check `/proc/sys/fs/file-nr` the first number is the current number of file descriptors in use.
---
### Author:  [@johnh](https://discourse.julialang.org/u/johnh)
#### Post date: [June 23, 2020, 7:36pm UTC](https://discourse.julialang.org/t/weird-error-systemerror-memory-mapping-failed-too-many-open-files-in-system/41944/3 "2020-06-23T19:36:41Z")
Can you log into one of your compute nodes, or submit a simple batch job and run
ulimit -a
I just did this on my Fedora laptop
open files (-n) 1024