UPX OPTIONS

On the main window, click OPTIONS icon.

On the Options dialog, select UPX tab.

    MODALITY

   Intelligent  (default)

Automatically selects and applies the algorithm
(NRV2E or LZMA) best suited to each file.

   NRV2E

Good compression, less risk of file damage.
Programs packed with NRV2E may have faster load  times than with LZMA.

Especially recommended for smaller files under 100 kb.

   LZMA

Best compression.  Slower decompression/load times.

More prone to compatibility problems or file damage.

Recommended for larger files.

    EXTRA

   Keep backup files  (OFF by default)

Although this is OFF by default, you may wish to enable it, in case packing breaks the application.  It might be easier to restore from backup than to unpack and test.

   Use Ultra-Brute compression ratio  (OFF by default)

The highest available compression.  Processing time will be slower.

There is more risk of file damage with this setting.

   Compress embedded icons  (ON by default)

Test to verify that icons still display correctly.  Sometimes compressed icons can no longer be accessed, causing incorrect icon display, or even program hangs.

   Compress resources  (ON by default)

Resources include bitmaps, cursors, dialogs, string tables.

Test to verify that all application elements display and function correctly.

   Compress export section  (ON by default)

This can improve compression ratio, but may not work with all programs.

Disable this setting if the program will be run under Wine.

   Strip relocation records  (ON by default)

Generally there is no need for a relocation table in an exe, since they are the first thing loaded and guaranteed to load at the preferred address, but stripping may break some exe's.  Usually the stripped files become smaller, but some files may become larger.

    UPX usage documentation can be found in the ATA source-file download.
or online on this Linux website.