sed 's/\(.*\) (nflg || \(.*\))\(.*\)/\1\2\3/' src/useradd.c.backup > src/useradd.c &&: This sed is used to fix a compilation bug which occurs due to a variable (nflg) being used but not defined. cp limits login.access /etc: These files were not installed during the installation of the package so we copy them manually as those files are used to configure authentication details on the system. sed "s%/var/spool/mail%/var/mail%" login.defs.linux > /etc/login.defs: /var/spool/mail is the old location of the user mailboxes. The location that is used nowadays is /var/mail. ln -sf vipw vigr and ln -sf vipw.8 vigr.8: According to the manpage of vipw, vigr should be a symlink to it. Because the shadow installation procedure doesn't create these symlinks, we create them manually.