# Sysimage file extension

**URL:** <https://discourse.julialang.org/t/sysimage-file-extension/59073>\
**Category:** Tooling\
**Tags:** sysimage\
**Created:** [April 12, 2021, 7:49am UTC](https://discourse.julialang.org/t/sysimage-file-extension/59073 "2021-04-12T07:49:53Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![TheLateKronos](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/thelatekronos/32/12824_2.png) [@TheLateKronos](https://discourse.julialang.org/u/TheLateKronos)\
**Post date:** [April 12, 2021, 7:49am UTC](https://discourse.julialang.org/t/sysimage-file-extension/59073/1 "2021-04-12T07:49:53Z")

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From [Creating a sysimage · PackageCompiler (julialang.github.io)](https://julialang.github.io/PackageCompiler.jl/dev/devdocs/sysimages_part_1/):  
“We start Julia with the `-Jsys.so` flag to load the new custom `sys.so` sysimage (or `sys.dylib` , `sys.dll` on macOS and Windows respecitively)”

I have successfully used the `.so` file extension on my windows computer, but I changed it to `.dll` based on this documentation. But If `.so` works on windows, where does it not work? Is the an advantage to using `.dll`? If I want to keep it as general as possible, should I use `.so`, becasue it works on Windows (my experience) and Linux (based on the quote from the docs)?

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**Author:** ![pfitzseb](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pfitzseb/32/45566_2.png) [@pfitzseb](https://discourse.julialang.org/u/pfitzseb)\
**Post date:** [April 12, 2021, 11:12am UTC](https://discourse.julialang.org/t/sysimage-file-extension/59073/2 "2021-04-12T11:12:11Z")

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The file extension doesn’t matter at all, it’s just that `so`/`dylib`/`dll` are the default extensions on Linux/MacOS/Windows.