Documentation/howto-debug.txt

   1 Debugging util-linux programs
   2 =============================
   3
   4 How to deal libtool
   5 -------------------
   6
   7 There are considerations to be made when profiling or debugging some programs
   8 found in the util-linux package. Because wrapper scripts are used for the
   9 binaries to make sure all library dependencies are met, you cannot use tools
  10 such as gdb or valgrind directly with them.
  11
  12 Let's take for example the mount command:
  13
  14         $> cd /path/to/util-linux
  15         $> file mount/mount
  16         mount/mount: Bourne-Again shell script text executable
  17
  18 The binary itself is located in the mount/.libs/ directory:
  19
  20         $> file mount/.libs/mount
  21         mount/.libs/mount: ELF 64-bit LSB executable, x86-64, version 1 \
  22         (SYSV), dynamically linked (uses shared libs) [...]
  23
  24 When this command is run, there's a library dependency error:
  25
  26         $> mount/.libs/mount
  27         mount/.libs/mount: /lib/libblkid.so.1: version `BLKID_2.20' not found \
  28         (required by mount/.libs/mount)
  29
  30 To overcome this we need set the LD_LIBRARY_PATH variable to read the path of
  31 the shared lib found in the sources, and not system-wide:
  32
  33         $> export LD_LIBRARY_PATH=$PWD/libblkid/src/.libs/:$LD_LIBRARY_PATH
  34
  35 Now external debugging tools can be run on the binary.
  36
  37 Happy hacking!
  38 Davidlohr Bueso, August 2011
  39
  40
  41 The libmount & libblkid
  42 -----------------------
  43
  44 Both of the libraries can be debugged by setting an environment variable
  45 consisting of a number. The number will be used as a bit mask, so the more 1 the
  46 higher the debugging level. Search for `DEBUG' from files
  47
  48         libblkid/src/blkidP.h
  49         libmount/src/mountP.h
  50
  51 to see what the different bits mean. At the time of writing this the following
  52 enabled full debug.
  53
  54         export LIBBLKID_DEBUG=all
  55         export LIBMOUNT_DEBUG=all
  56         export LIBFDISK_DEBUG=all
  57         export LIBSMARTCOLS_DEBUG=all
  58
  59 The libblkid reads by default /etc/blkid.conf which can be overridden by the
  60 environment variable BLKID_CONF. See manual libblkid/libblkid.3 for details
  61 about the configuration file.
  62
  63 Block device information is normally kept in a cache file (see blkid man page
  64 for more information about the cache file location) that can be overridden by
  65 the environment variable BLKID_FILE.
  66
  67 To libmount uses three paths, which can be overridden by using environment
  68 variables. Notice that these environment variables are ignored for non-root
  69 users.
  70
  71         env variable            if not set defaults to
  72         LIBMOUNT_FSTAB          /etc/fstab
  73         LIBMOUNT_MTAB           /etc/mtab
  74         LIBMOUNT_UTAB           /run/mount/utab or /dev/.mount/utab