What I think is happening is that the SetOptions statement in init.m is executed during kernel initialization as expected, however when the notebook window is opened, the front-end sets PageWidth to be WindowWidth. Furthermore, the kernel value does get changed accordingly whenever the window is resized.
This being the front-end, I would not be surprised if there are other/better ways, but what seemed to work was
SetOptions[$FrontEnd, PrivateEvaluationOptions -> {"OutputFormPageWidth" -> 125}]
While it was not the culprit in this question, I would still mention that something similar may happen in a console kernel session, where PageWidth can be reset by the terminal input library to be the width of the console at startup time. This can be avoided by either turning the terminal library off or using a scheduled task in init.m, e.g.
task := SetOptions["stdout", PageWidth -> 125];
RunScheduledTask[task, {1}]
so that it runs after the terminal library is loaded.
Internal\NewInput=False;toinit.m`. – ilian Jul 18 '15 at 15:57SetOptions["stdout", PageWidth -> 125];insideinit.mdoes not change thePageWidthsetting:Options["stdout", PageWidth]returns{PageWidth -> 32}after launching Mathematica. – Alexey Popkov Jul 18 '15 at 16:14SetOptions["stdout", PageWidth -> 125];andInternal\NewInput=False;`? – ilian Jul 18 '15 at 16:16task := SetOptions["stdout", PageWidth -> 125]; RunScheduledTask[task, {1}]. – ilian Jul 18 '15 at 17:02SetOptions["stdout", PageWidth -> 125];andInternal`NewInput=False;insideinit.m(at the same time), I have also triedtask := SetOptions["stdout", PageWidth -> 125]; RunScheduledTask[task, {1}]insideinit.m. Unfortunately both methods do not work andOptions["stdout", PageWidth]still returns{PageWidth -> 32}after launching Mathematica. I'm with MMa 10.2 on Win7 x64. With MMa 8.0.4 the situation is the same. – Alexey Popkov Jul 18 '15 at 17:56PageWidthtoWindowWidthand also change it dynamically on window resize. PerhapsSetOptions[$FrontEnd, {PrivateEvaluationOptions -> {"OutputFormPageWidth" -> 125}}]will do the trick? – ilian Jul 18 '15 at 19:44