(libc.info.gz) Notes on NSS Configuration File

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(libc.info.gz) NSS Configuration File

 
 29.2.3 Notes on the NSS Configuration File
 ------------------------------------------
 
 Finally a few more hints.  The NSS implementation is not completely
 helpless if '/etc/nsswitch.conf' does not exist.  For all supported
 databases there is a default value so it should normally be possible to
 get the system running even if the file is corrupted or missing.
 
    For the 'hosts' and 'networks' databases the default value is 'dns
 [!UNAVAIL=return] files'.  I.e., the system is prepared for the DNS
 service not to be available but if it is available the answer it returns
 is definitive.
 
    The 'passwd', 'group', and 'shadow' databases are traditionally
 handled in a special way.  The appropriate files in the '/etc' directory
 are read but if an entry with a name starting with a '+' character is
 found NIS is used.  This kind of lookup remains possible by using the
 special lookup service 'compat' and the default value for the three
 databases above is 'compat [NOTFOUND=return] files'.
 
    For all other databases the default value is 'nis [NOTFOUND=return]
 files'.  This solution give the best chance to be correct since NIS and
 file based lookup is used.
 
    A second point is that the user should try to optimize the lookup
 process.  The different service have different response times.  A simple
 file look up on a local file could be fast, but if the file is long and
 the needed entry is near the end of the file this may take quite some
 time.  In this case it might be better to use the 'db' service which
 allows fast local access to large data sets.
 
    Often the situation is that some global information like NIS must be
 used.  So it is unavoidable to use service entries like 'nis' etc.  But
 one should avoid slow services like this if possible.
 

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