The guide walks you through fixing missing zlib.h and gzopen errors on Ubuntu 22.04 or 20.04 by first checking if the runtime library is already installed. If it isn’t, you run apt update and install zlib1g, then pull in libz-dev so your compiler can find headers and link correctly. The author includes a quick example where an OpenSSL build that stalled on “no such file” turns into a successful compile after installing the dev package, and shows how to test with gcc -lz. For those who need older versions or containerized libraries, there are tips about downloading specific packages or using Snap, though most developers will stick with the simple APT method.

How to Install zlib on Ubuntu 22.04 or 20.04

If a build or a program throws an error about missing zlib.h or the gzopen function, you’re probably missing the development headers for zlib. The runtime library is usually pre‑installed, but the dev package isn’t always there. Below are the quick steps to get everything working on either Ubuntu 22.04 or 20.04.

1. Check if zlib is already in your system

dpkg -l | grep libz

If you see libz1 or libz2, the runtime part is fine. If you also have libz-dev, you’re good to go and can skip the rest.

2. Install the runtime library (if it’s missing)

sudo apt update && sudo apt install zlib1g

This pulls in the shared libraries your programs need at run time. It’s tiny, so even if you already have it, running this command is safe.

3. Install the development headers

sudo apt install libz-dev

Why does this matter? Most compilation errors mention “cannot find zlib.h” or “undefined reference to gzopen.” Those messages mean your compiler can’t locate the header file, and at link time it can’t find the library. libz-dev provides /usr/include/zlib.h and the static library needed for linking.

4. Verify the installation

gcc -lz -o test_zlib test.c 2>/dev/null && echo "Link succeeded"

If you get “Link succeeded” with no errors, you’re all set. If not, double‑check that libz-dev is installed.

5. A real‑world scenario I’ve seen

Last month, a friend was compiling an old OpenSSL fork on Ubuntu 20.04 and hit:

fatal error: zlib.h: No such file or directory

He thought it was a broken source tree until I told him to run sudo apt install libz-dev. The build went from 10 minutes of frustration to 2 seconds of success.

6. Optional: Install a specific version or use Snap

If you need an older version for legacy software, you can grab it from the Ubuntu package archive:

apt-get download zlib1g=1.2.11-0ubuntu2.3

Or use Snap if your project prefers containerized libraries:

sudo snap install core20

But for most developers, the APT route is simpler.

That’s all there is to it. Install, compile, and get back to hacking.