fakehostname - A Command To Fake Your Hostname!

Wow! Now you can run a command and fake your hostname!

tl;dr

Usage

Usage is relatively simple: fakehostname <new-hostname> <cmd> [<args> ...]

For example on Linux,

$ fakehostname joan hostname
joan

$ fakehostname rivers uname -n
rivers

Or you can use the library directly, ie with libfakehostname.so in the current directory,

$ LD_PRELOAD=./libfakehostname.so FAKE_HOSTNAME=joan-rivers hostname
joan-rivers

Note you can use fakehostname on macOS, but it's a little tricky and you should read the note below.

Installation

All Platforms (From Source)

Fetch the source from Github and install! You'll need git and GCC

git clone https://github.com/dtcooper/fakehostname.git
cd fakehostname
make
sudo make install

On Debian/Ubuntu Linux (From Source)

You can install the build requirements via,

sudo apt-get install -y git build-essential

And then run the commands above

On Debian/Ubuntu Linux (Prebuilt Package)

You can also install the package for the amd64 and arm64 architectures, which I've built and uploaded to the Releases Page.

Or try this fun single command which does the same,

wget -O - https://api.github.com/repos/dtcooper/fakehostname/releases/latest \
    | grep "browser_download_url.*$(dpkg --print-architecture).deb" | cut -d '"' -f 4 \
    | wget -i - -O /tmp/fhn.deb && sudo dpkg -i /tmp/fhn.deb && rm /tmp/fhn.deb

On Arch Linux

Install from the AUR, with an AUR helper. The example below uses Yay,

yay -S fakehostname

Overview

The command (fakehostname), and its associated library (libfakehostname), are a hack that slip between your program and the C standard library to monkey patch the uname and gethostname functions provided therein. This is accomplished via the LD_PRELOAD environment variables on Linux, and the DYLD_INSERT_LIBRARIES + DYLD_FORCE_FLAT_NAMESPACE evironment variables on macOS (see important note below). The library reads environment variable FAKE_HOSTNAME -- prepped by the command -- and uses that instead of your system's hostname.

This software has been tested on macOS 10.11 (El Capitan) and Ubuntu 16.04 LTS + 17.10.

Important Note for Apple's macOS (Darwin)

On macOS, starting with 10.11 (El Capitan), a feature called System Integrity Protection was introduced that disallows the dynamic insertion of libraries for system executables. One therefore can't use the environment variable DYLD_INSERT_LIBRARIES to actually use libfakehostname's implementation of the uname and gethostname.

You'll have to use executables that aren't in your system's path, ie /bin, /usr/bin, et cetera. For example, to use the hostname command, you'll have to copy it locally.

# Run on a Mac named "joan" and it doesn't work, since `hostname` is in /bin
$ fakehostname rivers hostname
joan

# So we copy the `hostname` command locally, and hurray, it works!
$ cp /bin/hostname .
$ fakehostname rivers ./hostname
rivers

Unfortunately, this renders this software relatively useless on macOS. Oh well!

Running The Tests

There a couple simple tests for the command, namely running uname and hostname and verifying it actually works.

make test

If all goes well, you should see a SUCCESS: All N/N tests passed! message!

Uninstalling

Uninstall with one command,

sudo make uninstall

Final Note

...and remember kids, have fun!

Author and License

This project was created by David Cooper and is licensed under the MIT License. See the LICENSE file for details.