Talk:Viber

Fix for Missing Libraries (v27.3.0.2)

Viber fails to launch on NixOS due to two issues: missing runtime libraries and a broken libxml2.so.2 symlink in the package.

Root Causes

1. Missing system libraries

Viber's NixOS package doesn't include several required runtime libraries (libxshmfence, libxcb-cursor, libxcb-util, pipewire).

2. Broken libxml2.so.2 symlink

The NixOS viber package creates a broken symlink:

opt/viber/lib/libxml2.so.2 -> /nix/store/.../libxml2-2.15.2/lib/libxml2.so

libxml2-2.15.2 only ships libxml2.so.16 (new ABI). Viber's bundled libQt6WebEngineCore.so.6 requires valuePush@@LIBXML2_2.4.30 from the old ABI, so it must be replaced with libxml2_13 (2.13.x).

Working Configuration

Replace pkgs.viber in environment.systemPackages with:

(pkgs.buildFHSEnv {
  name = "viber";
  targetPkgs = pkgs: [
    (pkgs.viber.overrideAttrs (old: {
      postFixup = (old.postFixup or "") + ''
        rm -f $out/opt/viber/lib/libxml2.so.2
        ln -s ${pkgs.libxml2_13.out}/lib/libxml2.so.2 $out/opt/viber/lib/libxml2.so.2
      '';
    }))
    pkgs.libxshmfence
    pkgs.libxcb-cursor
    pkgs.xcbutil
    pkgs.pipewire
  ];
  runScript = "viber";
  extraInstallCommands = ''
    mkdir -p $out/share/applications
    cp ${pkgs.viber}/share/applications/viber.desktop $out/share/applications/
    sed -i "s|Exec=.*|Exec=viber %u|" $out/share/applications/viber.desktop
    sed -i "s|Path=.*|Path=/opt/viber/|" $out/share/applications/viber.desktop
  '';
})

Why each package is needed

Package	Provides	Why needed
pkgs.libxshmfence	libxshmfence.so.1	Required by Viber's bundled Qt WebEngine
pkgs.libxml2_13.out	libxml2.so.2 (old ABI)	Replaces broken symlink; Viber's Qt needs valuePush@@LIBXML2_2.4.30
pkgs.libxcb-cursor	libxcb-cursor.so.0	Required by Qt 6.5+ xcb platform plugin
pkgs.xcbutil	libxcb-util.so.1	Required by Qt's xcb platform plugin (libQt6XcbQpa.so.6)
pkgs.pipewire	libpipewire-0.3.so	Qt multimedia audio support

Important Notes

• libxml2_13.out vs libxml2_13: The bare attribute resolves to the -bin output which contains no .so files. Always use .out.
• xcb-util vs xcbutil: Inside a NixOS config, use pkgs.xcbutil (no hyphen). nix eval nixpkgs#xcb-util works at the CLI but pkgs.xcb-util in a config file does not.
• Working directory: bwrap (used by buildFHSEnv) does not map /etc/nixos inside the sandbox. Launch viber from ~, not from /etc/nixos.

What Didn't Work

Approach	Why it failed
programs.nix-ld.libraries	Doesn't intercept library lookups for Viber's bundled libs
steam-run viber	Steam runtime doesn't include libxshmfence either
writeShellScriptBin with LD_LIBRARY_PATH	Leaks into Viber's own bundled libs causing libxml2 version conflicts
pkgs.libxml2_13 (bare)	Resolves to -bin output — symlink points nowhere
pkgs.xcb-util	Attribute doesn't exist in pkgs set; correct name is pkgs.xcbutil

Dusski (talk) 12:05, 15 July 2026 (UTC)