This is the contents of a "good" /etc/man.conf for CentOS6, in case anyone gets into this state (i.e. something wipes out /etc/man.conf and you are stuck because you can't read man pages!). Thank @JakeGould for pointing me in the right direction. In this case, the decompressor is lzma.
# # Generated automatically from man.conf.in by the # configure script. # # man.conf from man-1.6f # # For more information about this file, see the man pages man(1) # and man.conf(5). # # This file is read by man to configure the default manpath (also used # when MANPATH contains an empty substring), to find out where the cat # pages corresponding to given man pages should be stored, # and to map each PATH element to a manpath element. # It may also record the pathname of the man binary. [This is unused.] # The format is: # # MANBIN pathname # MANPATH manpath_element [corresponding_catdir] # MANPATH_MAP path_element manpath_element # # If no catdir is given, it is assumed to be equal to the mandir # (so that this dir has both man1 etc. and cat1 etc. subdirs). # This is the traditional Unix setup. # Certain versions of the FSSTND recommend putting formatted versions # of /usr/.../man/manx/page.x into /var/catman/.../catx/page.x. # The keyword FSSTND will cause this behaviour. # Certain versions of the FHS recommend putting formatted versions of # /usr/.../share/man/[locale/]manx/page.x into # /var/cache/man/.../[locale/]catx/page.x. # The keyword FHS will cause this behaviour (and overrides FSSTND). # Explicitly given catdirs override. # # FSSTND FHS # # This file is also read by man in order to find how to call nroff, less, etc., # and to determine the correspondence between extensions and decompressors. # # MANBIN /usr/local/bin/man # # Every automatically generated MANPATH includes these fields # MANPATH /usr/man MANPATH /usr/share/man MANPATH /usr/local/man MANPATH /usr/local/share/man MANPATH /usr/X11R6/man # # Uncomment if you want to include one of these by default # # MANPATH /opt/*/man # MANPATH /usr/lib/*/man # MANPATH /usr/share/*/man # MANPATH /usr/kerberos/man # # Set up PATH to MANPATH mapping # # If people ask for "man foo" and have "/dir/bin/foo" in their PATH # and the docs are found in "/dir/man", then no mapping is required. # # The below mappings are superfluous when the right hand side is # in the mandatory manpath already, but will keep man from statting # lots of other nearby files and directories. # MANPATH_MAP /bin /usr/share/man MANPATH_MAP /sbin /usr/share/man MANPATH_MAP /usr/bin /usr/share/man MANPATH_MAP /usr/sbin /usr/share/man MANPATH_MAP /usr/local/bin /usr/local/share/man MANPATH_MAP /usr/local/sbin /usr/local/share/man MANPATH_MAP /usr/X11R6/bin /usr/X11R6/man MANPATH_MAP /usr/bin/X11 /usr/X11R6/man MANPATH_MAP /usr/bin/mh /usr/share/man # # NOAUTOPATH keeps man from automatically adding directories that look like # manual page directories to the path. # #NOAUTOPATH # # NOCACHE keeps man from creating cache pages ("cat pages") # (generally one enables/disable cat page creation by creating/deleting # the directory they would live in - man never does mkdir) # #NOCACHE # # Useful paths - note that COL should not be defined when # NROFF is defined as "groff -Tascii" or "groff -Tlatin1"; # not only is it superfluous, but it actually damages the output. # For use with utf-8, NROFF should be "nroff -mandoc" without -T option. # (Maybe - but today I need -Tlatin1 to prevent double conversion to utf8.) # # If you have a new troff (version 1.18.1?) and its colored output # causes problems, add the -c option to TROFF, NROFF. # TROFF /usr/bin/groff -Tps -mandoc NROFF /usr/bin/nroff -c -mandoc 2>/dev/null EQN /usr/bin/geqn -Tps NEQN /usr/bin/geqn -Tutf8 TBL /usr/bin/gtbl # COL /usr/bin/col REFER /usr/bin/grefer PIC /usr/bin/gpic VGRIND GRAP PAGER /usr/bin/less -is BROWSER /usr/bin/less -is HTMLPAGER /bin/cat CAT /bin/cat # # The command "man -a xyzzy" will show all man pages for xyzzy. # When CMP is defined man will try to avoid showing the same # text twice. (But compressed pages compare unequal.) # CMP /usr/libexec/man-cmp.sh # # Compress cat pages # COMPRESS /usr/bin/lzma COMPRESS_EXT .lzma # # Default manual sections (and order) to search if -S is not specified # and the MANSECT environment variable is not set (1x-8x sections are used by # xorg packages). # MANSECT 1:1p:8:2:3:3p:4:5:6:7:9:0p:n:l:p:o:1x:2x:3x:4x:5x:6x:7x:8x # # Default options to use when man is invoked without options # This is mainly for the benefit of those that think -a should be the default # Note that some systems have /usr/man/allman, causing pages to be shown twice. # #MANDEFOPTIONS -a # # Decompress with given decompressor when input file has given extension # The command given must act as a filter. # .gz /usr/bin/gunzip -c .bz2 /usr/bin/bzip2 -c -d .lzma /usr/bin/unlzma -c -d .z .Z /bin/zcat .F .Y # # Enable/disable makewhatis database cron updates. # If MAKEWHATISDBUPDATES variable is uncommented # and set to n or N, cron scripts # /etc/cron.daily/makewhatis.cron # /etc/cron.weekly/makewhatis.cron # will not update makewhatis database. # Otherwise the database will be updated. # #MAKEWHATISDBUPDATES n MANPATH /opt/intel/mic/share/man