I don't know why, but the mouse (trackpoint) on the IBM A30 stopped working when I upgrade from kernel 2.4 to 2.6. I had to explicitly (i.e.
/etc/modules) load
mousedev and
psmouse and then change gpm's mouse type from
autops2 to
ps2 and then things worked OK.
I had a problem once trying to ssh from work to my machine at home. Everything worked fine until I left the connection idle for a while. When I hit a key I got
Read from remote host www.caboteria.org: Connection reset by peer Connection to www.caboteria.org closed.
Setting ssh's
KeepAlive parameter on the client and server didn't seem to do much good. I found a patch that helped, though:
http://www.sc.isc.tohoku.ac.jp/~hgot/sources/openssh-watchdog.html
The "contributed" patch at the bottom is close to the version that ships with Debian Potato, and although it gives errors when you try to apply it it's pretty small and relatively easy to cut-n-paste by hand.
This appeared in the RISKS digest:
Date: Thu, 22 Nov 2001 23:50:39 +0300 From: Diomidis Spinellis Subject: Risks of the space character in Unix filenames The root of the problem reported in the "Glitch in iTunes Deletes Drives (Solomon, RISKS-21.74)" article is the default way the Unix shell handles filenames with embedded spaces. Although a space can legally appear in a Unix filename, such an occurrence is not usual; Unix filenames tend to be terse, often even shorter than a single word, (e.g. "src", "doc", "etc", "bin") so they can be swiftly typed. A number of more recent and supposedly user-friendly operating systems like the Microsoft Windows family, and, I understand, the MacOS, use longer and more descriptive file names ("Documents and Settings", "Program Files"). Many of these filenames contain spaces; the ones I listed are by default used by Windows 2000 as the location to store user data and application files (the equivalent of /home/username and /bin under Unix). As Unix-style tools and relevant applications are increasingly ported to run under Windows (see for example [1, 2, 3] and my Windows outwit tool suite described in [4]) or natively run under Mac OS X, problems and associated Risks arise. The main reason is that some often-used Unix shell constructs fail when applied to filenames containing a space character. Unfortunately, these constructs appear in many existing programs, and even in the writings of the original system developers, who, in all fairness, could not have foreseen how their tools would have been used 25 years after their conception. Technically, the problem manifests itself when field splitting (the process by which the shell splits input into words) is naively applied on the output of an expansion that generates filenames with embedded spaces. Consider the following example, appearing on page 95 of one of the classic texts on Unix programming [5]: for i in ch2.* echo $i: diff -b old/$i $i echo done The above code will compare all files matching the ch2.* pattern in the current directory with copies presumably stored in the directory called "old". Consider what will happen when the code is applied to a file called "ch2.figure 3.dot" (notice the space between the word figure and the "3"). The shell variable i will be set to the correct filename, but then the shell will execute the "diff" command with the following argument list (customarily passed to C programs in the argv array): argv[0] = "diff" argv[1] = "-b" argv[2] = "old/ch2.figure" argv[3] = "3.dot" argv[4] = "ch2.figure" argv[5] = "3.dot" and diff will complain diff: extra operand as more than two filenames were passed as arguments. This happens, because words are expanded by most Unix shells in the following order: 1. Parameter (including variable) expansion, command substitution. 2. Field splitting. As a result, the variable $i is first expanded into "ch2.figure 3" and then the result is split into fields for further processing or for passing them as arguments to a command. The most common dangerous constructs that can appear in step 1 are variable references (e.g. $PATH, $word) and commands inside backquotes (e.g. `find . -type f -name 'ch2.*'`). These dangerous constructs are quite common, appearing among other places in the original article describing the Bourne shell [6] (for i in * do if test -d $d/$i [...]), in other scripts in the reference of the original example [5 p. 141, 143], and even in quite recent work by the same authors [7, p. 149]. It is also prevalent in existing operating system tools; I counted 43 occurrences of one suspicious pattern ("$*") in a NetBSD source tree, 8 in a FreeBSD command path, and 49 in the shell scripts of a Mandrake Linux distribution. The Unix world is definitely not ready to deal with filenames containing the space character. Avoiding this problem is not trivial. A radical solution would be to change the value of the shell's "internal field separator" (IFS) variable. This variable contains the characters that shell uses to split words. Its default value is ". This solution however would break more things than it would fix, since most scripts expect words to be separated by spaces. As an example the construct "A='ls -l';$A" would not work. The most practical solution is to manually enclose variables inside double quotes when using them in contexts where only a single word is normally expected. The shell will still expand the variable inside the quotes, but will treat the result as a single word. Thus the offending part in the original example should have been written as: diff -b "old/$i" "$i" In addition, whenever a shell script uses the variable $* to obtain the values of all parameters passed to a script, the $* variable should be replaced by the variable $@, again inside double quotes. Thus the common code pattern for arg in $* should be written as for arg in "$@" Interestingly, Kernighan and Pike were aware of the $* problem and the above solution since 1984; they aptly characterize the "$@" solution as "almost black magic" [5 p. 161]. Still, these changes will not correctly handle filenames with embedded whitespace returned from a command substitution. In this case, temporarily changing the IFS variable before executing a command may be the only feasible solution. The following example illustrates this approach: # Save original IFS OFS="$IFS" # Set IFS to newline IFS=' ' # The find command might output filenames with spaces wc -l `find . -type f` # Restore original IFS IFS="$OFS" By searching existing shell scripts for the patterns I described and applying the suggested changes most problems can be solved. Other scripting languages like Tcl and, to a lesser extend, Perl may also have problems dealing with filenames with spaces. Similar approaches (appropriate quoting in Perl "eval" blocks and use of the "list" command in Tcl) can be used to avoid these problems. References [1] David G. Korn. Porting Unix to Windows NT. In Proceedings of the USENIX 1997 Annual Technical Conference, Anaheim, CA, USA, January 1997. Usenix Association. [2] Geoffrey J. Noer. Cygwin32: A free Win32 porting layer for UNIX applications. In Proceedings of the 2nd USENIX Windows NT Symposium, Seattle, WA, USA, August 1998. Usenix Association. [3] Stephen R. Walli. OPENNT: UNIX application portability to Windows NT via an alternative environment subsystem. In Proceedings of the USENIX Windows NT Symposium, Seattle, WA, USA, August 1997. Usenix Association. [4] Diomidis Spinellis. Outwit: Unix tool-based programming meets the Windows world. In USENIX 2000 Technical Conference Proceedings, pages 149-158, San Diego, CA, USA, June 2000. Usenix Association. [5] Brian W. Kernighan and Rob Pike. The UNIX Programming Environment. Prentice-Hall, 1984. [6] S. R. Bourne. The UNIX shell. Bell System Technical Journal, 57(6):65-84 July/August 1978. (Also appears in volume 2 of the Unix Programmer's Manual and in AT & T, UNIX System Readings and Applications, volume I. Prentice-Hall, 1987.) [7] Brian W. Kernighan and Rob Pike. The Practice of Programming. Addison-Wesley, 1999. Diomidis Spinellis - http://www.dmst.aueb.gr/dds/ Athens University of Economics and Business (AUEB)
Info on diskless workstations:
http://www.ltsp.org/ - the linux terminal server project, folks who have a Linux distro that turns an old PC into a diskless X-terminal. It worked very well for me on an old Pentium 133.
http://lists.debian.org/debian-devel/2001/debian-devel-200104/msg00647.html I wasn't able to get reliable performance using the user-space nfs server (many "stale NFS handle" errors in apt-get, probably caused by moving files and trying to use the same handle) but it seems to be reliable using the kernel nfs server.
If you're using NFS you should sweep your filesystems periodically looking for old files named
.nfs*. These get left behind when a process has a file open, another process deletes it, and the first process crashes. See
http://www.sunmanagers.org/archives/1998/0229.html
See also
http://syslinux.hackerdojo.com/pxe.php if you've got a motherboard with a PXE bios.
If you're serving more than a couple of workstations then the default NFS parameters will probably cause bottlenecks. The NFS howto at
http://nfs.sourceforge.net/nfs-howto/ has a page about performance tuning. The number of instances of the server daemon is key.
2.6
Build kernel, need
CONFIG_IP_PNP=y,
CONFIG_ROOT_NFS=y, and of course the driver for the ethernet card should be built-in, i.e. not a module.
mknbi-linux --rootdir=rom --ip=dhcp arch/i386/boot/bzImage > /tmp/bzImage-2.6.4 sudo cp /tmp/bzImage-2.6.4 /tftpboot/lts/ make modules-install sudo mv /lib/modules/2.4.6 /usr/local/ltsp/dickless/lib/modules
SPAM Filtering
http://www.securitysage.com/guides/postfix_uce.html has detailed info on how to set up the Postfix MTA to filter spam.
HOWTO harden postfix to SPAM:
http://www.freesoftwaremagazine.com/articles/focus_spam_postfix/
At some point the nightly man-db update process started going into an endless loop using 100% CPU. I'm not sure what the problem was, but blowing away the database (
/var/cache/man) fixed it.
chroot
Two HOWTO's that I found useful for setting up
chroot jails are:
http://www.tjw.org/chroot-login-HOWTO/,
http://kegel.com/crosstool/current/doc/chroot-login-howto.html
grub
site -
http://www.gnu.org/software/grub/
manual -
http://www.gnu.org/software/grub/manual/
burn a CD -
http://www.gnu.org/software/grub/manual/html_node/Making-a-GRUB-bootable-CD_002dROM.html#Making-a-GRUB-bootable-CD_002dROM
a good way to scan the partitions is
find /grub/stage1 or
find /boot/grub/stage1 since that's about the shortest filename you can reliably look for in a grub installation.
The last time I messed with grub it was to get a USB drive to boot Linux. I had a lot of problems, from grub streaming "GRUB GRUB GRUB GRUB" messages infinitely to it just printing "GRUB" and then stopping. In my case it looks like the problem was that the disk order was different depending on whether the USB drive was being booted from or whether some other drive was. The fix was to
not use the "d" flag on the grub
install command.
When I installed Fedora 8 on a USB drive I had to boot from the grub cdrom and then
setup (hd1,0) (hd1,0).
if you're like me you'll probably blow away the windows MBR in the process, so here's how to fix it:
http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/bootcons_fixmbr.mspx
backup
rdiff-backup -
http://www.nongnu.org/rdiff-backup/docs.html
Python program that uses rdiff to generate efficient differential backups. Straightforward command line. Seems to use a lot of CPU.
rsnapshot -
http://www.rsnapshot.org/
Similar idea, written in perl. Seems to be more config-file oriented less command-line oriented.
http://www.mikerubel.org/computers/rsync_snapshots/ http://blog.interlinked.org/tutorials/rsync_time_machine.html
Hot-plug devices
When I was logged into
warthog and plugged Tory's ipod into its cradle, it would get mounted automagically. When Tory tried this it didn't work. It seems that the set of programs to manage things like ipods is pretty complicated, but there's some useful info at
http://www.freedesktop.org/wiki/Software/HalFAQ and especially
http://www.mythic-beasts.com/~mark/random/hal/.
In our case it turned out that Tory wasn't a member of the
plugdev group.
Hard Disk Spindown
I got a usb-attached disk drive to make backups to, and it spins the drive down after a while to save power. That's cool, but the problem is that Linux barfs when it tries to access the drive:
Apr 9 06:19:01 voom kernel: sd 0:0:0:0: Device not ready: <6>: Current: sense key: Not Ready
Apr 9 06:19:01 voom kernel: Additional sense: Logical unit not ready, initializing command required
Apr 9 06:19:01 voom kernel: end_request: I/O error, dev sda, sector 12375
This might help:
http://www.nslu2-linux.org/wiki/FAQ/DealWithAutoSpinDownOnSeagateFreeAgent
Mounting USB Devices
HAL is responsible for mounting USB drives when they're plugged in. It will use the partition's label as a mount point if it can or it will fall back to something like "disk".
http://www.debuntu.org/device-partition-labeling talks about how to set the labels.