After trying to reinstall courier to fix an inability to login, I get the following errors when attemtping apt-get -f install:

# apt-get -f install
Reading package lists... Done
Building dependency tree... Done
Correcting dependencies... Done
The following extra packages will be installed:
courier-authlib-userdb
The following NEW packages will be installed:
courier-authlib-userdb
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
8 not fully installed or removed.
Need to get 0B/33.4kB of archives.
After unpacking 86.0kB of additional disk space will be used.
Do you want to continue [Y/n]?
WARNING: The following packages cannot be authenticated!
courier-authlib-userdb
Authentication warning overridden.
(Reading database ... 142386 files and directories currently installed.)
Unpacking courier-authlib-userdb (from .../courier-authlib-userdb_0.58-4_i386.deb) ...
dpkg: error processing /var/cache/apt/archives/courier-authlib-userdb_0.58-4_i386.deb (--unpack):
unable to make backup link of `./usr/share/man/man8/userdbpw.8.gz' before installing new version: Operation not permitted
Errors were encountered while processing:
/var/cache/apt/archives/courier-authlib-userdb_0.58-4_i386.deb
du: cannot access `/usr/share/man/man8/mkfs.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/fdisk.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/sfdisk.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/cytune.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/smbd.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/mksmbpasswd.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/tdbbackup.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/nmbd.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/pdbedit.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/mount.smbfs.8.gz': Input/output error
du: cannot access `/usr/share/man/man1/g++-4.0.1.gz': Input/output error
du: cannot access `/usr/share/man/man1/lesspipe.1.gz': Input/output error
du: cannot access `/usr/share/man/man1/lessecho.1.gz': Input/output error
du: cannot access `/usr/share/man/man1/slogin.1.gz': Input/output error
du: cannot access `/usr/share/man/man1/xedit.1.gz': Input/output error
du: cannot access `/usr/share/man/man8/mkfs.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/fdisk.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/sfdisk.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/cytune.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/smbd.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/mksmbpasswd.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/tdbbackup.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/nmbd.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/pdbedit.8.gz': Input/output error
du: cannot access `/usr/share/man/man8/mount.smbfs.8.gz': Input/output error
du: cannot access `/usr/share/man/man1/g++-4.0.1.gz': Input/output error
du: cannot access `/usr/share/man/man1/lesspipe.1.gz': Input/output error
du: cannot access `/usr/share/man/man1/lessecho.1.gz': Input/output error
du: cannot access `/usr/share/man/man1/slogin.1.gz': Input/output error
du: cannot access `/usr/share/man/man1/xedit.1.gz': Input/output error
E: Sub-process /usr/bin/dpkg returned an error code (1)

Obviously something has run amock; see my other thread about libldap_r.so.2 problems, which were fixed as far as apache2 is concerned by restoring /usr/lib/libldap* links.

When I list /usr/share/man/man8/userdbpw.8.gz I get this wierd output. Check out the user/group numbers!

# ls -l /usr/share/man/man8/userdbpw.8.gz
p--xr-x--x 45025 3406276593 2817580240 2817492246 1969-12-31 16:00 /usr/share/man/man8/userdbpw.8.gz

and, furthermore.........

# mandb -c
Processing manual pages under /usr/share/man...
Updating index cache for path `/usr/share/man/man8'. Wait...gzip: /usr/share/man/man8/dumpe2fs.8.gz is not a directory or a regular file - ignored
mandb: command '/bin/gzip -dc /usr/share/man/man8/dumpe2fs.8.gz' failed with exit status 512
mandb: warning: /usr/share/man/man8/dumpe2fs.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/mkfs.8: No such file or directory
mandb: warning: /usr/share/man/man8/mkfs.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/fdisk.8: No such file or directory
mandb: warning: /usr/share/man/man8/fdisk.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/sfdisk.8: No such file or directory
mandb: warning: /usr/share/man/man8/sfdisk.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/userdbpw.8: No such file or directory
mandb: warning: /usr/share/man/man8/userdbpw.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/smbd.8: No such file or directory
mandb: warning: /usr/share/man/man8/smbd.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/mksmbpasswd.8: No such file or directory
mandb: warning: /usr/share/man/man8/mksmbpasswd.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/tdbbackup.8: No such file or directory
mandb: warning: /usr/share/man/man8/tdbbackup.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/nmbd.8: No such file or directory
mandb: warning: /usr/share/man/man8/nmbd.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/pdbedit.8: No such file or directory
mandb: warning: /usr/share/man/man8/pdbedit.8.gz: bad symlink or ROFF `.so' request
gzip: /usr/share/man/man8/smbspool.8.gz is not a directory or a regular file - ignored
mandb: command '/bin/gzip -dc /usr/share/man/man8/smbspool.8.gz' failed with exit status 512
mandb: warning: /usr/share/man/man8/smbspool.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/smbmnt.8: No such file or directory
mandb: warning: /usr/share/man/man8/smbmnt.8.gz: bad symlink or ROFF `.so' request
gzip: /usr/share/man/man8/mount.cifs.8.gz is not a directory or a regular file - ignored
mandb: command '/bin/gzip -dc /usr/share/man/man8/mount.cifs.8.gz' failed with exit status 512
mandb: warning: /usr/share/man/man8/mount.cifs.8.gz: bad symlink or ROFF `.so' request
gzip: /usr/share/man/man8/smbmount.8.gz is not a directory or a regular file - ignored
mandb: command '/bin/gzip -dc /usr/share/man/man8/smbmount.8.gz' failed with exit status 512
mandb: warning: /usr/share/man/man8/smbmount.8.gz: bad symlink or ROFF `.so' request
gzip: /usr/share/man/man8/smbumount.8.gz is not a directory or a regular file - ignored
mandb: command '/bin/gzip -dc /usr/share/man/man8/smbumount.8.gz' failed with exit status 512
mandb: warning: /usr/share/man/man8/smbumount.8.gz: bad symlink or ROFF `.so' request
gzip: /usr/share/man/man8/umount.cifs.8.gz is not a directory or a regular file - ignored
mandb: command '/bin/gzip -dc /usr/share/man/man8/umount.cifs.8.gz' failed with exit status 512
mandb: warning: /usr/share/man/man8/umount.cifs.8.gz: bad symlink or ROFF `.so' request
gzip: /usr/share/man/man8/mount.smb.8.gz is not a directory or a regular file - ignored
mandb: command '/bin/gzip -dc /usr/share/man/man8/mount.smb.8.gz' failed with exit status 512
mandb: warning: /usr/share/man/man8/mount.smb.8.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man8/mount.smbfs.8: No such file or directory
mandb: warning: /usr/share/man/man8/mount.smbfs.8.gz: bad symlink or ROFF `.so' request
Updating index cache for path `/usr/share/man/man1'. Wait...mandb: can't open /usr/share/man/man1/g++-4.0.1: No such file or directory
mandb: warning: /usr/share/man/man1/g++-4.0.1.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man1/lesspipe.1: No such file or directory
mandb: warning: /usr/share/man/man1/lesspipe.1.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man1/lessecho.1: No such file or directory
mandb: warning: /usr/share/man/man1/lessecho.1.gz: bad symlink or ROFF `.so' request
mandb: can't resolve /usr/share/man/man1/lessfile.1.gz: Input/output error
mandb: can't open /usr/share/man/man1/slogin.1: No such file or directory
mandb: warning: /usr/share/man/man1/slogin.1.gz: bad symlink or ROFF `.so' request
mandb: can't resolve /usr/share/man/man1/rlogin.1.gz: Input/output error
mandb: can't open /usr/share/man/man1/pycentral.1: No such file or directory
mandb: warning: /usr/share/man/man1/pycentral.1.gz: bad symlink or ROFF `.so' request
mandb: can't open /usr/share/man/man1/xedit.1: No such file or directory
mandb: warning: /usr/share/man/man1/xedit.1.gz: bad symlink or ROFF `.so' request
mandb: can't resolve /usr/share/man/man1/i486-linux-gnu-g++-4.0.1.gz: Input/output error
Updating index cache for path `/usr/share/man/man9'. Wait...done.
Checking for stray cats under /usr/share/man...
Checking for stray cats under /var/cache/man...
Processing manual pages under /usr/local/man...
Updating index cache for path `/usr/local/man/man1'. Wait...done.
Checking for stray cats under /usr/local/man...
Checking for stray cats under /var/cache/man/oldlocal...
Processing manual pages under /usr/local/share/man...
Updating index cache for path `/usr/local/share/man/man1'. Wait...done.
Checking for stray cats under /usr/local/share/man...
Checking for stray cats under /var/cache/man/local...
13 man subdirectories contained newer manual pages.
6089 manual pages were added.
0 stray cats were added.

a manual e2fsck (pressed return about 1000 times!) fixed all these errors.