magic file patch
here's a patch for your magic file (usually /usr/share/magic) to allow file(1) to do simple recognition of UPX compressed executables.
with this patch, running file on a UPX compressed executable you get the following (example) output:
$ file ./gimp
./gimp: ELF 32-bit LSB executable, UPX compressed, Intel 80386, version 1, statically linked, stripped
# apply this patch to /usr/share/magic to allow file(1) to have simple
# recognition of UPX (http://wildsau.idv.uni-linz.ac.at/mfx/upx.html)
# compressed executables
# do (with permissions to write to magic [eg. as root]):
# cp upx.magic.patch /usr/share && cd /usr/share && patch < upx.magic.patch
*** magic.old Sat May 8 04:49:47 1999
--- magic Thu May 13 18:02:18 1999
*** 1351,1356 ****
--- 1351,1358 ----
# What're the correct byte orders for the nCUBE and the Fujitsu VPP500?
# updated by Daniel Quinlan (firstname.lastname@example.org)
+ # UPX (http://wildsau.idv.uni-linz.ac.at/mfx/upx.html) support added
+ # by Jay Johnston (email@example.com)
0 string \177ELF ELF
>4 byte 0 invalid class
>4 byte 1 32-bit
*** 1360,1365 ****
--- 1362,1368 ----
>>16 leshort 0 no file type,
>>16 leshort 1 relocatable,
>>16 leshort 2 executable,
+ >>>154 string UPX UPX compressed,
>>16 leshort 3 shared object,
# Core handling from Peter Tobias
# corrections by Christian 'Dr. Disk' Hechelmann
To quote your description of UPX on Freshmeat (see the top of this page) and at the top of your documentation for UPX:
"Your executables [when compressed with UPX] suffer no memory overhead or other drawbacks"
While UPX excels at its function, it does create drawbacks for the executables it compresses. I was just clarifying that for those looking at the freshmeat description of UPX (using the comments section for what it's there for).
Furthermore, UPX is a closed-source program, so the only way one in the Linux community can help others in regards to UPX's drawbacks is to spread the knowledge of those drawbacks (as opposed to helping to solve them as one would do if the program was Open Source and gpl'd).