In UNIX-like OS, which is the correct meaning of the command chmod u+x foo?

The chmod command syntax is chmod [who][operator][permission] file. Here, u means "user" (owner), + means "add", and x means "execute". So u+x adds execute permission specifically to the owner. Option D is incorrect because chmod u+x only modifies the owner's permission without removing execute permission from others; it's a pure addition operation.

Step-by-step Derivation:
Breaking down chmod u+x foo:

• u = user (file owner)
• + = add/grant permission
• x = execute permission
• foo = target file

Result: Execute permission is added ONLY to the owner. Other users' permissions remain unchanged. This matches option A exactly. Option B refers to g (group), option C refers to a (all), and option D incorrectly claims removal of permissions from others, which doesn't happen with the + operator.