diff options
Diffstat (limited to 'login/README.utmpd')
| -rw-r--r-- | login/README.utmpd | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/login/README.utmpd b/login/README.utmpd new file mode 100644 index 0000000000..d70b3d8de2 --- /dev/null +++ b/login/README.utmpd @@ -0,0 +1,174 @@ +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 10 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 <bugs@gnu.org>. + +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. |