a simpler non-latex example
wr.tex
%%%
aaaa
\newwrite\wfile
\immediate\openout\wfile=\jobname.aux
\immediate\write\wfile{boo}
bbb
\bye
%%
if you run this once so a .aux file is written, then
chmod a-w wr.aux
to remove write permission, then using pdftex and hitting return on error
produces:
$ pdftex wr
This is pdfTeX, Version 3.141592653-2.6-1.40.29 (TeX Live 2026) (preloaded
format=pdftex)
restricted \write18 enabled.
entering extended mode
(./wr.tex
! I can't write on file `wr.aux'.
l.5 \immediate\openout\wfile=\jobname.aux
(Press Enter to retry, or Control-D to exit; default file extension is
`.tex')
Please type another output file name:
! I can't write on file `wr.aux'.
l.5 \immediate\openout\wfile=\jobname.aux
(Press Enter to retry, or Control-D to exit; default file extension is
`.tex')
Please type another output file name:
! I can't write on file `wr.aux'.
l.5 \immediate\openout\wfile=\jobname.aux
(Press Enter to retry, or Control-D to exit; default file extension is
`.tex')
Please type another output file name:
! I can't write on file `wr.aux'.
l.5 \immediate\openout\wfile=\jobname.aux
(Press Enter to retry, or Control-D to exit; default file extension is
`.tex')
Please type another output file name:
and it loops until you give it a file that it can write to.
with luatex you get
$ luatex wr
This is LuaTeX, Version 1.24.0 (TeX Live 2026)
restricted system commands enabled.
(./wr.tex
! I can't write on file `wr.aux'.
l.5 \immediate\openout\wfile=\jobname.aux
Please type another output file name:
[1{/usr/local/texlive/2026/texmf-var/fonts/map/pdftex/updmap/pdftex.map}])</usr
/local/texlive/2026/texmf-dist/fonts/type1/public/amsfonts/cm/cmr10.pfb>
Output written on wr.pdf (1 page, 9886 bytes).
Transcript written on wr.log.
and the source file is over-written.
David
