each character doubled in inputfield in build but not editor on ubuntu 16.04

same issue here. i tried debugging unity's InputField and it appears that the Event.PopEvent loop gets two keyDown events instead of one... i guess the problem is related to some change they did to the native code that deals with xlib events on linux. guess I'm gonna be opening a bug report since they don't have a public source to check and I'm not too good at reverse engineering /shrug

here is a temporary horrible workaround for the issue. if you want to be sure it doesn't break when they change InputField's internals you are better off making an entire copy of the class with the workaround.

 using UnityEngine.Events;
 using UnityEngine.EventSystems;
 using UnityEngine.UI;
 using System.Reflection;
 
 // a horrible hack to work around input duplication bugs on linux
 public class InputFieldWithWorkarounds : InputField {
 
     int keyDownCount = 0;
     bool workAroundDuplicatedKeystrokesBug = false;
 
     static FieldInfo GetPrivateFieldObject(string name) {
         return typeof(InputField).GetField (
             name, BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.Instance
         );
     }
 
     void SetPrivateField(string name, System.Object value) {
         GetPrivateFieldObject (name).SetValue (this, value);
     }
 
     System.Object GetPrivateField(string name) {
         return GetPrivateFieldObject (name).GetValue (this);
     }
 
     bool m_ShouldActivateNextUpdate {
         set { SetPrivateField ("m_ShouldActivateNextUpdate", (System.Object)value); }
         get { return (bool)GetPrivateField ("m_ShouldActivateNextUpdate"); }
     }
 
     Event m_ProcessingEvent {
         set { SetPrivateField ("m_ProcessingEvent", (System.Object)value); }
         get { return (Event)GetPrivateField ("m_ProcessingEvent"); }
     }
 
     void ActivateInputFieldInternal() {
         MethodInfo method = typeof(InputField).GetMethod(
             "ActivateInputFieldInternal", BindingFlags.NonPublic | BindingFlags.Instance
         );
         method.Invoke(this, new object[] {});
     }
 
     protected override void Start () {
         base.Start ();
         workAroundDuplicatedKeystrokesBug = Application.unityVersion == "2017.3.0f1"
             && Application.platform == RuntimePlatform.LinuxPlayer;
     }
     
     public override void OnUpdateSelected(BaseEventData eventData)
     {
         if (!workAroundDuplicatedKeystrokesBug) {
             base.OnUpdateSelected (eventData);
             return;
         }
 
         // Only activate if we are not already activated.
         if (m_ShouldActivateNextUpdate)
         {
             if (!isFocused)
             {
                 ActivateInputFieldInternal();
                 m_ShouldActivateNextUpdate = false;
                 return;
             }
 
             // Reset as we are already activated.
             m_ShouldActivateNextUpdate = false;
         }
 
         if (!isFocused)
             return;
 
         bool consumedEvent = false;
         while (Event.PopEvent(m_ProcessingEvent))
         {
             Event ev = m_ProcessingEvent;
             if (ev.rawType == EventType.KeyDown)
             {
                 if (ev.keyCode != KeyCode.Return && keyDownCount++ % 2 != 0) {
                     continue;
                 }    
 
                 consumedEvent = true;
                 var shouldContinue = KeyPressed(ev);
                 if (shouldContinue == EditState.Finish)
                 {
                     DeactivateInputField();
                     break;
                 }
             }
         }
 
         if (consumedEvent)
             UpdateLabel();
 
         eventData.Use();
     }
 }

This is a known regression. The bug is tracked here: https://issuetracker.unity3d.com/issues/linux-keystrokes-recorded-twice If you are affected by this issue, please upvote the issuetracker page. (lolisamurai's bug report posted in comments was closed as a duplicate)