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Diffstat (limited to 'Documentation/howto-debug.txt')
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diff --git a/Documentation/howto-debug.txt b/Documentation/howto-debug.txt new file mode 100644 index 0000000..6936eb5 --- /dev/null +++ b/Documentation/howto-debug.txt @@ -0,0 +1,74 @@ +Debugging util-linux programs +============================= + +How to deal libtool +------------------- + +There are considerations to be made when profiling or debugging some programs +found in the util-linux package. Because wrapper scripts are used for the +binaries to make sure all library dependencies are met, you cannot use tools +such as gdb or valgrind directly with them. + +Let's take for example the mount command: + + $> cd /path/to/util-linux + $> file mount/mount + mount/mount: Bourne-Again shell script text executable + +The binary itself is located in the mount/.libs/ directory: + + $> file mount/.libs/mount + mount/.libs/mount: ELF 64-bit LSB executable, x86-64, version 1 \ + (SYSV), dynamically linked (uses shared libs) [...] + +When this command is run, there's a library dependency error: + + $> mount/.libs/mount + mount/.libs/mount: /lib/libblkid.so.1: version `BLKID_2.20' not found \ + (required by mount/.libs/mount) + +To overcome this we need set the LD_LIBRARY_PATH variable to read the path of +the shared lib found in the sources, and not system-wide: + + $> export LD_LIBRARY_PATH=$PWD/libblkid/src/.libs/:$LD_LIBRARY_PATH + +Now external debugging tools can be run on the binary. + +Happy hacking! +Davidlohr Bueso, August 2011 + + +The libmount & libblkid +----------------------- + +Both of the libraries can be debugged by setting an environment variable +consisting of a number. The number will be used as a bit mask, so the more 1 the +higher the debugging level. Search for `DEBUG' from files + + libblkid/src/blkidP.h + libmount/src/mountP.h + +to see what the different bits mean. At the time of writing this the following +enabled full debug. + + export LIBBLKID_DEBUG=all + export LIBMOUNT_DEBUG=all + export LIBFDISK_DEBUG=all + export LIBSMARTCOLS_DEBUG=all + +The libblkid reads by default /etc/blkid.conf which can be overridden by the +environment variable BLKID_CONF. See manual libblkid/libblkid.3 for details +about the configuration file. + +Block device information is normally kept in a cache file (see blkid man page +for more information about the cache file location) that can be overridden by +the environment variable BLKID_FILE. + +To libmount uses three paths, which can be overridden by using environment +variables. Notice that these environment variables are ignored for non-root +users. + + env variable if not set defaults to + LIBMOUNT_FSTAB /etc/fstab + LIBMOUNT_MTAB /etc/mtab + LIBMOUNT_UTAB /run/mount/utab or /dev/.mount/utab |