With the introduction of version 2 of the GNU C Library the format of the UTMP and WTMP files changed for some configurations (see Q&A `Why does getlogin() always return NULL on my Linux box?' of the FAQ). This version of the GNU C Library contains a solution for the problems this may cause, by providing an UTMP daemon `utmpd'. Do I need it? ============= If your configuration is one of the following: i[3456]86-*-linux-gnu Linux-2.0 on Intel m68k-*-linux-gnu Linux-2.0 on Motorola 680x0 you might need it, so please read on. If it is not, please read the section titled `Programming' at the end of this text. In principle, you only need the daemon if you want to keep using old programs linked against the previous version of the Linux C Library (libc5). In addition you will need the daemon if you are running Linux on Intel, and you are planning to use iBCS (Intel Binary Compatibility Standard). If you have no libc5 programs left on your system and you are not using iBCS, it is probably better not to install the daemon since it uses (a small amount of) memory and CPU time. But apart from that it shouldn't hurt to install `utmpd', so when in doubt install it anyway. Installation ============ The installation process (`make install') already places the `utmpd' binary in $(sbindir). The only thing you have to do is modifying your startup scripts to start the daemon. Unfortunately this is a bit of a hassle, since the layout of these scripts is not standardized. You should try to find the command that creates the file `/var/run/utmp'. This is usually done in a script named `/etc/rc', `/etc/init.d/boot' (Debian) or `/etc/rc.d/rc.S' (Slackware). You could try: grep utmp /etc/* /etc/init.d/* /etc/rc.d/* to find the right script. The creation of `/var/run/utmp' is usually done with a command like: : > /var/run/utmp or cat /dev/null > /var/run/utmp Now add a line before this command to create the file `/var/run/utmpx' e.g. : > /var/run/utmpx or cat /dev/null > /var/run/utmpx whatever you prefer, and after this command, add a line to start the daemon utmpd The entire fragment could look something like # Clean up /var/run and create /var/run/utmp so that we can login. ( cd /var/run && find . ! -type d -exec rm -f -- {} \; ) : > /var/run/utmpx : > /var/run/utmp utmpd If the file `/var/log/wtmp' exists on your system, you will probably want to create the file `/var/log/wtmpx'. Programs linked against the GNU C Library will now write to `/var/log/wtmpx', while programs linked against the old library will continue to write to `/var/log/wtmp'. Of course this means that the information gets spread over two files. We hope to provide a better solution in the future. After a reboot, user accounting should be working again. If not, please refer to the section titled `Troubleshooting' below before submitting a bug report. What is `utmpd' doing? ====================== After installation there will be two files that store the user accounting information: `/var/run/utmp' and `/var/run/utmpx'. The file `/var/run/utmp' will be in the old format so libc5 programs will continue to work (even if they are broken and do not use the library functions to access the user accounting database). And on Intel, you can safely link `/var/run/utmp' to `/etc/utmp' for iBCS programs. Programs linked against the new GNU C Library (glibc2) will contact the daemon for all user accounting database access. The daemon will store its information in `/var/run/utmpx' and keeps this file in sync with `/var/run/utmp'. Entries added to `/var/run/utmpx' will be converted to the old format and will be added to `/var/run/utmp' and vice versa. This way both libc5 and glibc2 see the same information in the same fields of `struct utmp'. Of course libc5 programs see only part of the information that glibc2 programs see because not all members of the glibc2 `struct utmp' are present in the libc5 `struct utmp'. For the same reason libc5 will see a truncated version of those fields where the length of the glibc2 field is larger than the corresponding libc5 field (ut_user, ut_line, ut_host). Troubleshooting =============== If user accounting is not working on your system, e.g. programs like `who' or `logname' return rubbish, or you cannot login, make sure that: * The file `/var/run/utmpx' exists. * The file `/var/log/wtmpx' exists. * No program linked against the GNU C Library (libc6) is accessing `/var/run/utmp' directly (see the section on `Programming' below). If that does not solve your problems, please use the `glibcbug' script to report the problem to . The `utmpd' daemon uses `syslogd' to report problems. It uses the `daemon' facility and `warning' and `error' levels. Alternatively you could use the following option to ease debugging: `--debug' Use this option if you want the daemon to output its warnings and error messages to the terminal instead of sending them to the system logger (`syslogd'). When using this option the daemon does not auto-background itself. To use this option you should first kill the daemon that is already running, and start a fresh one with the desired option: kill `cat /var/run/utmpd.pid` utmpd --debug Please include any warnings or error messages from `utmpd' in your bug reports. Programming =========== In order for the `utmpd' approach to work it is essential that NO program EVER accesses the UTMP and WTMP files directly. Instead, a program should use ONLY the available library functions: * utmpname() Select the database used (UTMP, WTMP, ...). * setutent() Open the database. * getutent() Read the next entry from the database. * getutid() Search for the next entry with a specific ID. * getutline() Search for the next entry for a specific line. * pututline() Write an entry to the database. * endutent() Close the database. * updwtmp() Add an entry to a database (WTMP, ...). For details, please refer to `The GNU C Library Reference Manual', which also contains information about some additional functions derived from BSD and XPG that may be of interest. The command info libc "User Accounting Database" should point you at the right location. If you encounter a program that reads from or, even worse, writes to the UTMP and WTMP files directly, please report this as a bug to the author of that program. Note that the files referred to by the macros `_PATH_UTMP' and `_PATH_WTMP' might even disappear in the future, so please do not use these, except in a call to `utmpname()' or `updwtmp()', not even to check their existence.