gww@aphasia.UUCP (George Williams) (08/27/85)
We have here a callan box (modified by someone else if that matters) running
system 5 unix (no source of course, we have 4.2bsd source on a vax if that can
be modified). The box is of the opinion that its uuname is `clm' we would like
to convince it otherwise; there does not seem to be a hostname command, or any
equivalent. One system V that we have has a magic little file that lives in
/usr/lib/uucp that contains this name, does callan?
It seems to me that I read somewhere that the host name was compiled into
the kernel under sysV, that seems dumb, and unbelievable (we don't have source).
What am I missing?
George Williams
decvax!frog!aphasia!gww
There must be a better way.guy@sun.uucp (Guy Harris) (08/31/85)
> The box is of the opinion that its uuname is `clm' we would like to > convince it otherwise; there does not seem to be a hostname command, or any > equivalent. One system V that we have has a magic little file that lives in > /usr/lib/uucp that contains this name, does callan? > > It seems to me that I read somewhere that the host name was compiled > into the kernel under sysV, that seems dumb, and unbelievable (we don't > have source). It may or may not be dumb and unbelievable, but it is true. Given the environment that the USG/USDL UNIX releases were, until recently, targeted at (namely, AT&T sites who had source, and who ran big machines with a wide variety of possible hardware configurations, so you'd build a kernel specifically for that machine), it's not that dumb. The intent is that the distribution would come with a "generic" kernel, whose sole purpose was to run on just about any configuration long enough to build a kernel tailored for your configuration. At that time you'd assign a name to the system and build a kernel with that name built in. A company offering S5 on their machine could, if AT&T's binary licensing terms permit it (I don't know whether they do or not - they *should*, but that's no guarantee), offer the contents of "/usr/src/uts/<machine>/cf" as part of their distribution, along with pre-compiled object libraries for the kernel. That's sufficient to build a tailored kernel and to set the system name. This solution fails to some degree in the case of 4.xBSD, where you may build a kernel which isn't completely generic but which will run on several machines (using the autoconfiguration code), and fails miserably in the case of the small UNIX boxes where there are a limited number of possible hardware configurations and where you may not trust the end user to be able to configure a kernel. Some micro vendors have a command that'll either patch your /unix (or whatever it's called) or your running kernel or both to give the system a particular name. If any such micro vendors didn't do this, but instead kludged up all the user-mode programs which want the system name to get it out of a file, they didn't do a very good job. CCI originally did that until I got fed up and hacked the "uname" command to patch the kernel if you have it a name as an argument. If you want, you can patch it yourself using "adb" (or, if you're feeling ambitious, write a program to do it). The structure returned by a "uname" system call is called "utsname". Unless the vendor has monkeyed with it, it consists of 5 (or 4, for System III) 9-character strings; the strings are embedded in the structure, not pointed to by pointers in the structure. Starting at the location "utsname" (or "_utsname", as is likely on most systems), there will be 9 bytes which will probably be the system name. The next 9 bytes after it (starting at "utsname + 9") will definitely be the system name unless something is badly screwed up. Just patch those to the name you want - remember to include the terminating '\0' (if the first string isn't the current system name, don't patch it). Remember to make a copy of the kernel before doing this, and remember to reboot afterwards if you only patched it and not /dev/kmem. It may not be optimal, but it's a lot better than, say, V7, where you needed all the source to do a sysgen (many V7 vendors changed this, but out of the box you needed source) *and* the name of the system was not affected by a sysgen - it came out of an include file and was compiled directly into user-mode programs (many V7 vendors fixed this, also). Guy Harris
joe@emacs.uucp (Joe Chapman) (09/01/85)
<> > [ Referring to a SysV-derived system ] > It seems to me that I read somewhere that the host name was compiled > into the kernel under sysV, that seems dumb, and unbelievable (we don't > have source). You can poke around for the utsname structure (its format should be in the documentation for uname(1) or uname(2)) with your favorite debugger and change your hostname to whatever you'd like. My favorite method is to Emacs up the kernel, and do a Query Replace on the hostname---count those ^@'s right or you'll be in trouble. Do this casually while one of your colleagues is looking and become a legend in your own time. Of course, now I do ``emacs /dev/kmem'' instead of ps... :-) -- -- Joseph Chapman decvax!cca!emacs!joe CCA Uniworks, Inc. emacs!joe@cca-unix.ARPA 20 William St. Wellesley, MA 02181 (617) 235-2600
tim@cithep.UucP (Tim Smith ) (09/01/85)
Sounds like a job for adbman! Look at location utsname in /unix. There
you will find a string with the name of the machine ( actually, you will
find TWO strings with the name of the machine. I forget which one you
need to change. Better do them both ). Change these strings with adb.
I think they are eight character strings, null terminated iff less than
eight chars long.
--
unlk a6
rts
Tim Smith
ihnp4!{wlbr!callan,cithep}!timjww@sdcsvax.UUCP (Joel West) (09/01/85)
> Sounds like a job for adbman! Look at location utsname in /unix. There > you will find a string with the name of the machine ( actually, you will > find TWO strings with the name of the machine. I forget which one you > need to change. Better do them both ). Change these strings with adb. Actually, the 2nd is the uucp name. But not knowing who wrote what sloppy code, I wouldn't be brave enough to run a system with the 1st <> 2nd. Joel West CACI, Inc. - Federal (c/o UC San Diego) {ucbvax,decvax,ihnp4}!sdcsvax!jww jww@SDCSVAX.ARPA