When using ArcIMS on AIX platform, output images that are generated by ArcIMS Spatial Server do not always honor the umask setting.
ArcIMS Spatial Server, specifically the MapServer.dll sets permissions on the output image that it writes to the disk in response to a GET_IMAGE request. When setting access privileges on the output image, in addition to setting the permissions as defined in umask, it also applies execute privilege on the output image for users that are allowed read or write access as per the umask setting. This is a known limitation of ArcIMS Spatial Server on AIX.
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