关于`file`命令解释器含义及Ubuntu16.04调试版Perl无法执行的技术问询

Hey there, let's tackle your two questions step by step:

1. What does the interpreter reported by the file command refer to? #

When the file command mentions an "interpreter", it's talking about the program the OS uses to launch or execute the target file. There are two key scenarios:

• For script files (like Perl, Bash, or Python scripts), this refers to the program specified in the shebang line (#!) at the top of the file—for example, #!/usr/bin/perl tells the OS to use /usr/bin/perl to parse and run the script. The file command reads this line to report the interpreter.
• For dynamically linked ELF binary files (compiled programs like the system's default Perl), this refers to the dynamic linker (e.g., /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 on 64-bit Ubuntu). The dynamic linker handles loading all shared libraries the binary depends on, setting up the runtime environment, and then starting the program itself.

In short, it's the "middleman" the OS relies on to get the file up and running.

2. Troubleshooting the non-executable debug Perl on Ubuntu 16.04 #

From your description, the truncated file output mentioning "存在空..." (empty...) almost certainly points to a missing or empty PT_INTERP segment in the debug Perl binary's ELF header. This segment stores the path to the dynamic linker (interpreter)—without it, the exec* system calls can't figure out how to load the binary, hence the "not executable" error.

Here's how to diagnose and fix this:

First, confirm the issue #

Run the full file command on the debug Perl binary to get the complete picture:

file /usr/lib/debug/usr/bin/perl

Look for phrases like "no interpreter", "interpreter: none", or references to an empty PT_INTERP segment. Compare this to the output of your system's working stripped Perl:

file /usr/bin/perl

You'll see a line like interpreter /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 in the working version—this is what's missing in the debug build.

Why this happens #

Files under /usr/lib/debug are often pure debug symbol files, not standalone executable binaries. While the perl-debug package claims to provide an unstripped Perl version, it's possible this binary was built without a valid interpreter path, or it's meant to be used as a symbol source rather than run directly.

How to fix it #

You don't actually need to run the debug binary directly to debug Perl. Here are two better approaches:

1. Debug the system Perl with gdb (recommended)
   Use your system's existing stripped Perl, and gdb will automatically load the debug symbols from /usr/lib/debug:

   gdb /usr/bin/perl
   

   Once gdb starts, you can set breakpoints, inspect variables, and debug just like you would with an unstripped binary.

2. Manually specify the dynamic linker (if you must run the debug binary)
   If you really need to execute the unstripped debug version, you can call the dynamic linker directly and pass the debug Perl binary as an argument. First, get the linker path from your working Perl (via file /usr/bin/perl), then run:

   /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 /usr/lib/debug/usr/bin/perl
   

   Replace the linker path with the one specific to your system (32-bit systems will have a different path, like /lib/ld-linux.so.2).

3. Check file permissions (just in case)
   Make sure the debug binary has executable permissions:

   ls -l /usr/lib/debug/usr/bin/perl
   

   If there's no x in the permissions column, add it with sudo chmod +x /usr/lib/debug/usr/bin/perl—though this won't fix the interpreter issue, it's a quick check to rule out obvious problems.

内容的提问来源于stack exchange，提问作者Greg Nisbet