oss-fuzz/docs/fuzzer_environment.md

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# Fuzzer environment on ClusterFuzz
Your fuzz targets will be run on a [Google Compute Engine](https://cloud.google.com/compute/) VM (Linux) with some security restrictions.
## Runtime Dependencies
You should not make any assumptions on the availability of dependent packages
in the execution environment. Packages that are installed via
[Dockerfile](https://github.com/google/oss-fuzz/blob/master/docs/new_project_guide.md#dockerfile)
or built as part of
[build.sh](https://github.com/google/oss-fuzz/blob/master/docs/new_project_guide.md#buildsh)
are not available on the bot runtime environment (where the fuzz targets run).
If you need these dependencies in the runtime environment, you can either
- Install the packages via Dockerfile
([example](https://github.com/google/oss-fuzz/blob/master/projects/tor/Dockerfile#L19))
and then link statically against them
([example](https://github.com/google/oss-fuzz/blob/master/projects/tor/build.sh#L40))
- Or build the dependencies statically in
[build.sh](https://github.com/google/oss-fuzz/blob/master/docs/new_project_guide.md#buildsh)
([example](https://github.com/google/oss-fuzz/blob/master/projects/ffmpeg/build.sh#L26)).
All build artifacts needed during fuzz target execution should be inside the `$OUT`
directory. Only those artifacts are archived and used on the bots. Everything else
is ignored (e.g. artifacts in `$WORK`, `$SRC`, etc) and hence is not available
in the execution environment.
You should ensure that the fuzz target works correctly by using `run_fuzzer` command
(see instructions [here](new_project_guide.md#testing-locally)). This command uses
a clean base-runner docker container and not the base-builder docker container
created during build-time.
## argv[0]
You must not modify argv[0]. It is required for certain things to work correctly.
## Current working directory
You should not make any assumptions about the current working directory of your
fuzz target. If you need to load data files, please use `argv[0]` to get the
directory where your fuzz target executable is located.
## File system
Everything except `/tmp` is read-only, including the directory that your fuzz target
executable lives in.
`/dev` is also unavailable.
## Hardware
Your project should not be compiled with `-march=native` or `-mtune=native`
flags, as the build infrastructure and fuzzing machines may have different CPUs
as well as other hardware differences. You may however use `-mtune=generic`.
## Network access
There will be no network interfaces available (not even loopback).