Wednesday, 14 January 2015

Checking symbols/functions in *nix binary library so/a files

What the man page says - "Nm  displays  the  name  list (symbol table) of each object file in the argument list."

If you want to list the symbols or function names in the binary library you can see their names using this command.

nm  opt/hadoop-2.4.0/lib/native/

If you have to check whether there is support for snappy in your hadoop binary do this:
nm  opt/hadoop-2.4.0/lib/native/ | grep -i snappy

And you should see something like this:
Java_org_apache_hadoop_io_compress_snappy_SnappyCompressor_compressBytesDirect0000000000003960 T Java_org_apache_hadoop_io_compress_snappy_SnappyCompressor_initIDs0000000000003bb0 T Java_org_apache_hadoop_io_compress_snappy_SnappyDecompressor_decompressBytesDirect0000000000003f60 T Java_org_apache_hadoop_io_compress_snappy_SnappyDecompressor_initIDs0000000000206cf0 b dlsym_snappy_compress0000000000206d20 b dlsym_snappy_uncompress

Without these Java native methods being compiled and available in the, MR runtime will also complain that "native snappy library not available".

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