The cause of this issue is that Shader Graph is installed in both Packages and Assets, which causes compilation errors due to duplicate assemblies.
---

Since Unity released it's Linux Editor for Unity 2018.1, for some reason, the shader graph doesn't work. It always gives the pink "Error" shader as the output.
Here is the output from the console:

Assembly with name 'Unity.ShaderGraph.Editor' already exists (Packages/com.unity.shadergraph/Editor/Unity.ShaderGraph.Editor.asmdef)

Assembly with name 'Unity.ShaderGraph.Editor' already exists (Assets/ShaderGraph-master/com.unity.shadergraph/Editor/Unity.ShaderGraph.Editor.asmdef)

Assertion failed: Assertion failed on expression: 'm_ScriptCache != NULL && m_ScriptCache->klass'

ArgumentException: Can not deserialize (UnityEditor.Experimental.Rendering.LightweightPipeline.LightWeightPBRSubShader), type is invalid
UnityEditor.Graphing.SerializationHelper.Deserialize[IPBRSubShader] (JSONSerializedElement item, System.Collections.Generic.Dictionary`2 remapper, System.Object[] constructorArgs) (at /home/trikha/.config/unity3d/cache/packages/packages.unity.com/com.unity.shadergraph@1.1.4-preview/Editor/Data/Util/SerializationHelper.cs:103)
UnityEditor.Graphing.SerializationHelper.Deserialize[IPBRSubShader] (IEnumerable`1 list, System.Collections.Generic.Dictionary`2 remapper, System.Object[] constructorArgs) (at /home/trikha/.config/unity3d/cache/packages/packages.unity.com/com.unity.shadergraph@1.1.4-preview/Editor/Data/Util/SerializationHelper.cs:153)
UnityEditor.ShaderGraph.Drawing.MaterialGraphEditWindow:Initialize(String)
ShaderGraphImporterEditor:ShowGraphEditWindow(String) (at /home/trikha/.config/unity3d/cache/packages/packages.unity.com/com.unity.shadergraph@1.1.4-preview/Editor/Importers/ShaderGraphImporterEditor.cs:42)
ShaderGraphImporterEditor:OnOpenAsset(Int32, Int32) (at /home/trikha/.config/unity3d/cache/packages/packages.unity.com/com.unity.shadergraph@1.1.4-preview/Editor/Importers/ShaderGraphImporterEditor.cs:51)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

{}
UnityEditor.ShaderGraph.Drawing.MaterialGraphEditWindow:Initialize(String)
ShaderGraphImporterEditor:ShowGraphEditWindow(String) (at /home/trikha/.config/unity3d/cache/packages/packages.unity.com/com.unity.shadergraph@1.1.4-preview/Editor/Importers/ShaderGraphImporterEditor.cs:42)
ShaderGraphImporterEditor:OnOpenAsset(Int32, Int32) (at /home/trikha/.config/unity3d/cache/packages/packages.unity.com/com.unity.shadergraph@1.1.4-preview/Editor/Importers/ShaderGraphImporterEditor.cs:51)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

This is happening on Windows 64bit Unity 2018.1.1f1 Shader Graph 1.1.6 as well.

Console log:
Assertion failed: Assertion failed on expression: 'success' UnityEditor.ShaderGraph.Drawing.MaterialGraphEditWindow:Initialize(String) ShaderGraphImporterEditor:ShowGraphEditWindow(String) (at C:/Users/vexti/AppData/Local/Unity/cache/packages/packages.unity.com/com.unity.shadergraph@1.1.6-preview/Editor/Importers/ShaderGraphImporterEditor.cs:42) ShaderGraphImporterEditor:OnOpenAsset(Int32, Int32) (at C:/Users/vexti/AppData/Local/Unity/cache/packages/packages.unity.com/com.unity.shadergraph@1.1.6-preview/Editor/Importers/ShaderGraphImporterEditor.cs:51) UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

Preview shader for graph has 1 error: Shader compilation error in graph at line 9 (on d3d11): failed to open source file: 'CoreRP/ShaderLibrary/Common.hlsl' Compiling Vertex program Platform defines: UNITY_ENABLE_REFLECTION_BUFFERS UNITY_USE_DITHER_MASK_FOR_ALPHABLENDED_SHADOWS UNITY_PBS_USE_BRDF1 UNITY_SPECCUBE_BOX_PROJECTION UNITY_SPECCUBE_BLENDING UNITY_ENABLE_DETAIL_NORMALMAP SHADER_API_DESKTOP UNITY_COLORSPACE_GAMMA UNITY_LIGHT_PROBE_PROXY_VOLUME UNITY_LIGHTMAP_FULL_HDR

(Note that the previews remain pink even if the procedural textures are disconnected)