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Path: senator-bedfellow.mit.edu!bloom-beacon.mit.edu!gatech!howland.reston.ans.net!cs.utexas.edu!mavrick!basto@cactus.org From: basto@cactus.org (Luis Basto) Newsgroups: comp.unix.aix,news.answers,comp.answers Subject: AIX Frequently Asked Questions (Part 2 of 3) Summary: This posting contains a list of Frequently Asked Questions and their answers about AIX, IBM's version of Unix. Keywords: AIX RS/6000 questions answers Message-ID: <1473@mavrick.UUCP> Date: 15 Nov 93 06:30:49 GMT Expires: 15 Dec 93 01:23:45 GMT Sender: luis@mavrick.UUCP Reply-To: basto@cactus.org (Luis Basto) Followup-To: comp.unix.aix Lines: 1594 Approved: news-answers-request@MIT.Edu Supersedes: <1463@mavrick.UUCP> Xref: senator-bedfellow.mit.edu comp.unix.aix:32877 news.answers:14709 comp.answers:2652 Archive-name: aix-faq/part2 Last-modified: November 15, 1993 Version: 2.43 Version: $Id: aix.faq,v 2.43 93/11/15 basto $ Frequently Asked Questions to AIX 3.x and IBM RS/6000 _____________________________________________________ 1.200: Some info about tape backups From: Craig Anderson The following supplements the information on rmt devices in InfoExplorer. It is based on my own personal experience with IBM tape drives running on AIX 3.1. No warranty is expressed or implied. CONFIGURING THROUGH SMIT: BLOCK size (0=variable length) (ALL) Sets the tape block size. When reading, the block size must be set to the block size set when the tape was written. When using some commands, tapes written with ANY block size can be read if the block size is set to 0 (variable length) (see "BLOCK SIZES" below). Use DEVICE BUFFERS during writes (ALL) Set to yes, the device will buffer data internally on writes. This greatly improves performance, but under certain cases may be undesirable since the data is not written to tape before returning a good indication. Use EXTENDED file marks (8mm only) Extended file marks take up much more space than short (or non-extended) file marks. But extended file marks can be overwritten, allowing data not at the beginning of tape to be overwritten (see "FILE MARKS" below). RETENSION on tape change or reset (1/4" only) If set to "no" then the tape will not be retentioned automatically when the tape is inserted. Note that this will take effect only after the device is used. FILE MARKS: Tape devices support multiple tape files. Tape files are the result of a backup/cpio/tar/dd type command, where the device is opened, written to, and closed. Because tapes allow large quantities of data to be written on a single tape, several backups (that is, tape files), may be combined on one physical tape. Between each tape file is a "tape file mark" or simply "file mark". These file marks are used by the device driver to indicate where one tape file ends and another begins. B E <------- O O -------> T T __ ____________________________ _______________ physical | \ | | \ |physical beginning| \ | tape | \ | end of | \ | file | \ | of tape | \ | mark | \ | tape |_____\________|_______|__________\_________| Note that there is a distinction between the beginning of tape (BOT) side of a file mark and the end of tape (EOT) side of a file mark. If the head is on the BOT side of a file- mark, "tctl fsf 1" command will move only to the EOT side of the same file mark. With the 1/4" tape drive, writing can only take place sequentially, or after blank tape has been detected. You cannot write over data on the tape (except at BOT). If you wish to add data to a tape which has been written and then rewound you should space forward file mark until an error occurs. Only then can you start writing again. With an 8mm tape drive, writing can only take place before blank tape, an EXTENDED file mark, or at BOT. Thus if several backups have been made on one tape and you wish to overwrite one of the backups, position the tape to the place you wish to start writing and issue the following commands: tctl bsf 1 tctl eof 1 The first command skips back to the BOT side of the same file mark. The second command rewrites the file mark (writing is allowed before extended file marks). The erase head will erase data ahead of the write head, so that after writing the file mark the head will be positioned before blank tape. Only after this may you start writing over data in the middle of the tape. (All data beyond where you are currently writing will be lost). Note that you cannot write over short file marks. In order for this to work, the tape must have been written with extended file marks (use smit to change this). With the 9-track drive writing can take place anywhere on the tape although overwriting single blocks of data is not supported. On the 8mm drive extended filemarks use 2.2 megabytes of tape and can take up to 8.5 seconds to write. Short filemarks use 184K and take up to 1.5 seconds to write. BLOCK SIZES: When data is written to tape it is written in blocks. The blocks on a tape are separated by inter-record gaps. It is important to understand the structure of the written tape in order to understand the problems which can occur with changing block sizes. In fixed block size mode all blocks on the tape are the same size. They are the size of the block size set in the device configuration. All read()s and write()s to the tape drive must be a multiple of the fixed block size. In fixed block mode a read() will return as many blocks as needed to satisfy the read() request. If a file mark is encountered while reading the tape only the data up until the file mark will be returned. It is not possible for the tape drive to read a tape whose block size is not the same as the block size in the device configuration. (Unless the device configuration is in variable size blocks.) In variable block size (0) mode, the blocks written on the tape are the size of the read() and write() requests to the device driver. In this case, the actual block sizes on the tape can be changed using the options to the backup commands (tar -C, cpio -C, backup -C). In variable mode, read() requests greater than size of the block on the tape will return only the data from the next block on the tape. It is this feature that allows tapes written in any block size (fixed or variable) to read with the dd command (the output from the dd command may be piped to restore, tar, or cpio for example.) Note that backup, tar, and cpio cannot read all tapes by using a large block size because they assume there is an error if they get a short read(). dd ibs=128k obs=16k if=/dev/rmt0 | ... The tape head is always positioned at an inter-record gap, file mark, or blank tape after reading or writing. With the 8mm tape drive, using a fixed block size which is not a multiple of 1K is inefficient. The 8mm tape drive always writes internally in 1K blocks. It simulates the effect of variable block sizes, but, for example, using a fixed block size of 512 bytes (or using variable block size and write()ing 512 bytes at a time) wastes one half of the tape capacity and gives only one half the maximum transfer rate. EXCHANGING DATA WITH NON-UNIX AND OTHER VENDORS MACHINES: Many tape drives support both variable and fixed block sizes. Variable block mode writes block sizes the size of the write command issued (tar and backup specify this with the -b option). In fixed mode, block sizes are fixed and all writes must be a multiple of the fixed block size. Unix often internally chops larger reads and writes up into manageable pieces (often 65535, 65534, or 65532 bytes) before doing the actual reads and writes. This means reads and writes of 64K bytes are often broken up into a 65535 byte record and a 1 byte record (In fixed mode the write will fail). Block sizes >= 64K (-C128 and greater) should be avoided for this reason. AIX does not break up read and write requests, but be aware of the situation on other machines. If the tape is written in an unknown block size then set the device configuration in smit to use variable size blocks, use the "dd" command with a large input block size, and pipe it to the restore command. For example: chdev -l rmt0 -a block_size=0 dd if=/dev/rmt0 ibs=128k obs=16k | tar -tvf- 1.201: How do I do remote backup? There seems to be several ways of doing this. I found the following works: tar -b1 -cf - . | rsh REMOTEHOST "dd ibs=512 obs=1024 of=/dev/TAPEDEVICE" From: kraemerf@franvm3.VNET.IBM.COM (Frank Kraemer) mksysb will not back up to remote tape devices. The following script will do remote backups. [Ed.: I've verified this script works fine. However, it may be slow for large filesystems since it creates a temp file of filenames in /tmp.] #!/bin/ksh # @(#) Create a backup tape of the private user data. #=================================================================# # Script : usave.sh # # Author : F. Kraemer # # Date : 92/02/19 # # Update : 92/10/29 # # Info : the ultimative backup script # # Example: usave.sh /dev/rmt0 - save to local tape # # usave.sh /save/save.me - save to local file # # usave.sh /tmp/pipe - save to remote tape # #-----------------------------------------------------------------# PS4="(+) " #set -x PROG=$(basename $0) HOST=$(hostname) TODAY=$(date +%H:%M:%S) # # cleanup # cleanup () { ec=$1 error=$2 case "$ec" in "$USAGE_EC") # usage error error="Usage:\t$PROG DeviceName\n" 1>&2 ;; "$NOTAP_EC") # Tape error error="error:\t$PROG: $DEVICE is not available on the system.\n" 1>&2 ;; "$LISTE_EC") # list error error="error:\t$PROG: could not create tar list for $LOGNAME.\n" 1>&2 ;; "$NOTAR_EC") # tar command error error="error:\t$PROG: tar command failed.\n" 1>&2 ;; "$PIPEP_EC") # pipe error error="error:\t$PROG: mknod command failed.\n" 1>&2 ;; "$NORSH_EC") # rsh error error="error:\t$PROG: rsh - Remote Shell command failed.\n" 1>&2 ;; "$RHOST_EC") # remote host error error="error:\t$PROG: Remote Host unknown.\n" 1>&2 ;; *) ;; esac case "$DEVICE" in # # Fix the block size if $DEVICE is a tape device # /dev/rmt[0-9]*) echo "\n\t$PROG: Rewinding tape to begin.........(please wait)\n" tctl -f $DEVICE rewind 2>/dev/null ;; *) ;; esac rm -f ${LIST} ${PIPE} 2>/dev/null [ -n "$error" ] && echo "\n${error}\n" trap '' 0 1 2 15 exit "$ec" } # # Variables # USAGE_EC=1 # exit code for usage error NOMNT_EC=2 # exit code wrong device name NOTAP_EC=3 # exit code no tape available LISTE_EC=4 # exit code backup list error NOTAR_EC=5 # exit code for wrong tar TRAPP_EC=6 # exit code for trap PIPEP_EC=7 # exit code for pipe RHOST_EC=8 # exit code for bad ping NORSH_EC=9 # exit code for bad rsh DEVICE="$1" # device to tar into LIST="/tmp/.tar.$LOGNAME.$$" # REMOTEH="" # Remote host for backup REMOTET="" # Remote tape for backup tapedev= # PIPE="/tmp/pipe" # Pipe for remote backup # # main() # tput clear echo "\n\t$PROG started from $LOGNAME@$HOST on $TERM at $TODAY.\n" rm -f $LIST 2>/dev/null # # Trap on exit/interrupt/break to clean up # trap "cleanup $TRAPP_EC \"Abnormal program termination. $PROG"\" 0 1 2 15 # # Check command options # [ "$#" -ne 1 ] && cleanup "$USAGE_EC" "" # # Check device name # [ `expr "$DEVICE" : "[/]"` -eq 0 ] && cleanup "$NOMNT_EC" \ "$PROG: Backup device or file name must start with a '/'." # # Check tape device # case "$DEVICE" in # # Fix the block size if $DEVICE is a tape device # /dev/rmt[0-9]*) # echo "\n\t$PROG: Verify backup media ($DEVICE)............\n" # # see if a low or high density tape device was specified # (eg rmt0.1) density="`expr $DEVICE : \ "/dev/rmt[0-9]*\.$[0-9]*$"`" # # strip /dev/ from device name and # get the base name (eg translate: # /dev/rmt0.2 to rmt0) # tapedev="`expr $DEVICE : \ "/dev/$rmt[0-9]*$[\.]*[0-9]*"`" # # Check if the tape is defined in the system. lsdev -C -c tape -S Available -F "name" | grep $tapedev >/dev/null 2>&1 rc=$? [ "$rc" -ne 0 ] && cleanup "$NOTAP_EC" "" # # Restore old tape name. # [ "${density:-1}" -lt 4 ] && density=1 || density=5 DEVICE="/dev/${tapedev}.${density}" echo "\n\t$PROG: Insert a tape in ($DEVICE)........(press enter)\n" read TEMP echo "\n\t$PROG: Rewinding tape to begin...........(please wait)\n" tctl -f $DEVICE rewind 2>/dev/null ;; # # Backup is done on remote host. The remote shell facility # must be set up and running. # ${PIPE}*) # echo "\n\t$PROG: Assuming remote backup via network.\n" echo "\t$PROG: Enter name of Remote Host ===> \c" read REMOTEH echo "\n\t$PROG: Pinging Remote Host to test connection.\n" ping ${REMOTEH} 1 1 >/dev/null 2>&1 rc=$? # give up unknown host [ "$rc" -ne 0 ] && cleanup "$RHOST_EC" "" JUNK=$(rsh ${REMOTEH} "/usr/sbin/lsdev -C -c tape -S Available") rc=$? # give up rsh failed [ "$rc" -ne 0 ] && cleanup "$NORSH_EC" "" echo "\t$PROG: Available Tapes on ${REMOTEH} are :\n\n\t\t${JUNK}\n" echo "\t$PROG: Enter name of Remote Tape (e.g. /dev/rmt0) ===> \c" read REMOTET echo "\n\t$PROG: Insert tape on ${REMOTEH} in ${REMOTET}..(press enter)" read TEMP echo "\t$PROG: Rewinding Remote Tape ${REMOTET} on ${REMOTEH}.\n" rsh ${REMOTEH} "tctl -f ${REMOTET} rewind" rc=$? # give up rsh failed [ "$rc" -ne 0 ] && cleanup "$NOTAP_EC" "" rm -f ${PIPE} 2>/dev/null mknod ${PIPE} p rc=$? # give up mknod failed [ "$rc" -ne 0 ] && cleanup "$PIPEP_EC" "" cat ${DEVICE} | rsh ${REMOTEH} "dd of=${REMOTET} obs=100b 2>/dev/null" & ;; *) ;; esac # # Prepare the list # echo "\n\t$PROG: Create list of files to be saved...." find $HOME -print > $LIST rc=$? [ "$rc" -ne 0 ] && cleanup "$LISTE_EC" "" # # tar the files # echo "\n\t$PROG: Changing current directory to (/)...." cd / > /dev/null 2>&1 echo "\n\t$PROG: Running tar format backup from user ($LOGNAME)...." tar -cvf "$DEVICE" -L "$LIST" rc="$?" [ "$rc" -ne 0 ] && cleanup "$NOTAR_EC" "" # # Backup completed # TODAY=$(date +%H:%M:%S) echo "\n\t$PROG ended at $TODAY............................\n\n" cleanup 0 1.202: How do I backup a multi-disk volume group? From: pack@acd.ucar.edu (Daniel Packman) [ Ed.: I have not verified this procedure. I would actually recommend NOT to have one volume group span multiple disks unless you really need such big logical volumes. ] 1. If you have a set of three or more disks in a volume group (typically 3 for 5xx machines with three internal drives; with only two, the procedures outlined here have to be modified to ignore the fact that you don't have a quorum in the volume group) 2. If one drive has failed (usually only one fails at a time :-) ) It is possible to go through a service boot (the volume group is called rootvg and one of the 2 good disks on it is called hdisk0): importvg -y rootvg hdisk0 varyonvg -f -n -m1 rootvg These commands will work, but give error messages. If you wish to mount a user filesystem, say /u on logical volume /dev/lv00, then mount -f /dev/lv00 /v will work only if jfslog, the journaled file system log device, is not on the damaged disk. If it is, you must (and can in any case) mount the filesystem read-only: mount -f -r /dev/lv00 /v This crucial and rather obvious point baffled several level 3 support personnel at Austin as well as myself for almost a week. Once the file system(s) of interest are available, they can be saved to tape for restoration later. Of course, one can expect only about two thirds of a filesystem to be recoverable if it spans all 3 physical disks. One other point to remember is that the standard boot procedure from floppy includes the restore command but does not include the backup command. ***************************************************************************** * If you do not have other RS6000 machines at your site it is imperative * * that you either build a bootable tape which includes either restore or * * tar or cpio (a bootable floppy set will not have enough space) or at the * * very least copy onto a spare floppy backup, cpio, or tar. The floppy * * should be created with backup -ivq so that its contents can be read into * * the memory resident system after booting. * ***************************************************************************** All is not lost if tar, cpio or backup are available on an undamaged disk that can be mounted. Since tar and cpio are in /bin, they may both very well be unavailable. It is a very good idea for those who have tape devices to build a bootable tape with their desired extra commands in it. Follow the instructions from IBM but add your desired commands to the following three files: /usr/lpp/bosinst/tape2 /usr/lpp/bosinst/diskette/boot2 /usr/lpp/bosinst/diskette/inslist If you have anything other than a minimum memory configuration, you should be able to add many commands. 1.203: How do I put multiple backups on a single 8mm tape? From: kerm@mcnc.org (Cary E. Burnette) There are two possible solutions to this, both of which use /dev/rmt0.1 which is non-rewinding. SOLUTION #1 ----------- To put multiple backups on a single tape, use /dev/rmt0.1, which is a no-rewind device, using either rdump or backup (both by name & inode work). Using rdump or backup "byinode" both generate the message that the tape is rewinding but actually do not. This is an example that works on my system: # rsh remote1 -l root /etc/rdump host:/dev/rmt0.1 -Level -u /u # rsh remote2 -l root /etc/rdump host:/dev/rmt0.1 -Level -u /u # tctl -f /dev/rmt0.1 rewind # rewinds the tape where I am implementing the command from host. To restore a table of contents of the first I would use # restore -f /dev/rmt0.1 -s1 -tv where the -s1 flag tells restore to go to the first record on the tape. Type the exact command again to get the second record. The -s(Number) means go to Number record from this spot. It works pretty well. SOLUTION #2 ----------- Steve Knodle Educational Resources Center Clarkson University I use: ------------------- Dump.sh -------------------- CONTENTSFILE=`date |dd conv=lcase |sed -e 's/19//' |awk '{print $6 $2 $3}'` set -x LEVEL=$1 shift backup -c -b 56 -$LEVEL -uf /dev/rmt0.1 / backup -c -b 56 -$LEVEL -uf /dev/rmt0.1 /usr backup -c -b 56 -$LEVEL -uf /dev/rmt0.1 /u tctl -f /dev/rmt0 rewind touch /usr/local/dumps/Contents.$CONTENTSFILE echo "Dumping /" >>/usr/local/dumps/Contents.$CONTENTSFILE restore -t -s 1 -f /dev/rmt0.1 >>/usr/local/dumps/Contents.$CONTENTSFILE echo "Dumping /usr" >>/usr/local/dumps/Contents.$CONTENTSFILE restore -t -q -s 1 -f /dev/rmt0.1 >>/usr/local/dumps/Contents.$CONTENTSFILE echo "Dumping /u" >>/usr/local/dumps/Contents.$CONTENTSFILE restore -t -q -s 1 -f /dev/rmt0.1 >>/usr/local/dumps/Contents.$CONTENTSFILE tctl -f /dev/rmt0 rewind I process the table-of-contents first by a little program that does common prefix encoding, and then compress. This gives a table of contents file I can keep on-line until the tape is reused. 1.204: How can I make an exact duplicate of a tape over the network? The challenge here is not to have to create a temporary file (disk space limitation) and work across heterogeneous networks. This script might work: LOCAL=/dev/tape_dev REMOTE=/dev/tape_dev dd if=$LOCAL ibs=64k obs=512 | rsh remote_host dd ibs=512 obs=64k of=$REMOTE From: pack@acd.ucar.edu (Daniel Packman) Daniel provides the following perl script to convert from the known world's function codes to AIX for compatibility. #!/bin/perl # Wrapper to convert input rmt requests to # AIX 3.2 ioctl numbers. We pass on all commands we don't understand # I0 MTWEOF -> I10 STWEOF write and end-of-file record # I1 MTFSF -> I11 STFSF forward space file # I2 MTBSF -> I12 STRSF reverse space file # I3 MTFSR -> I13 STFSR forward space record # I4 MTBSR -> I14 STRSR reverse space record # I5 MTREW -> I6 STREW rewind # I6 MTOFFL -> I5 STOFFL rewind and unload tape # I7 MTNOP -> I0 (no-op? should ignore following count) # I8 MTRETEN-> I8 STRETEN retension tape, leave at load point # I9 MTERASE-> I7 STERASE erase tape, leave at load point #I10 MTEOM (position to end of media ... no ibm equivalent?) #I11 MTNBSF (backward space file to BOF ... no ibm equivalent?) @iocs = (10,11,12,13,14,6,5,0,8,7); open(RMT,"|/usr/sbin/rmt") || die "Can't open pipe to rmt\n"; select(RMT); $| = 1; while (<STDIN>) { s/(^I)(\d$)/I$iocs[$2]/; exit 0 if $_ =~ /^[Qq]/; print RMT $_ ; } exit 0; 1.205: What is tape block size of 0? From: benson@odi.com (Benson I. Margulies) Tape devices are generally split into two categories: fixed block and variable block. 1/4" tape is the fixed block, and 8mm is variable. On a fixed block size device, the kernel always sends data to the device in suitable block size lumps, and varying the size passed to write(2) (e.g., via the bs option to dd) gives the kernel more data to stream. On a variable block size device, the kernel writes to the device whatever passed to it. On an 8mm, it had better be a multiple of 1024 to get efficient tape usage. AIX has the World's Only Variable Block Size 1/4" tape drive. If you use SMIT to set the block size to a nonzero value, AIX treats the device as fixed block size, whether it is or not. By default, 8mm drives are set to the same size as 1/4", 512 bytes. This is wasteful, but otherwise mksysb and installp would fail. If you set the block size to 0, the device is treated as variable block size, and the size passed to write becomes the physical block size. Then if you use a sensible block size to dd, all should be wonderful. 1.206: Resetting a hung tape drive From: Craig_Anderson@kcbbs.gen.nz (Craig Anderson) A process accesses the tape drive. The process stops, exits, or whatever, but still hold on to the drive. When this happens, the process cannot be killed by any signal and the tape drive cannot be used by any other process until the machine is rebooted. The following should help: RESET: AIX, like most UNIX systems has no reset function for tape drives. You can however send a Bus Device Reset (a standard SCSI message) to the tape drive using the following piece of code. If the tape drive does not respond to the BDR, then a SCSI Bus Reset will be sent (and this will reset every device on the SCSI Bus). SCSI Bus resets are rather extreme so you should refrain from using this program unnecessarily. But there are times (like after you've inserted a jammed/old/bad tape in an 8mm drive), when there's no other way to reset the device other than to shutdown and reboot (obviously you can power down and up an external drive to reset it - and this would be the better choice). This is actually documented in info, but can be hard to find and there's no complete program. /* taperst: resets the tape drive by sending a BDR to the drive. */ #include <stdio.h> #include <fcntl.h> #include <errno.h> #include <sys/scsi.h> int main(int argc, char **argv) { /* This can be run only by root */ if (argc != 2) { fprintf(stderr, "Usage: %s /dev/rmt#\n", argv[0]); return 1; } if (openx(argv[1], O_RDONLY, 0, SC_FORCED_OPEN) < 0) { perror(argv[0]); return 2; } return 0; } ______________________________________________________________________________ 1.300: Some info about the memory management system From: Michael Coggins (MCOG@CHVM1.VNET.IBM.COM). 1. Does AIX use more paging space than other unix systems? Under many scenarios, AIX requires more paging space than other unix systems. The AIX VMM implements a technique called "early allocation of paging space". When a page is allocated in RAM, and it is not a "client" (NFS) or a "persistent" (disk file) storage page, then it is considered a "working" storage page. Working storage pages are commonly an application's stack, data, and any shared memory segments. So, when a program's stack or data area is increased, and RAM is accessed, the VMM will allocate space in RAM and space on the paging device. This means that even before RAM is exhausted, paging space is used. This does not happen on many other unix systems, although they do keep track of total VM used. Example 1: Workstation with 64mb RAM is running only one small application that accesses a few small files. Everything fits into RAM, including all accessed data. On AIX, some paging space will already be used. On other unix systems, paging space will be 100% free. Clearly, this is an example that shows where we use more paging space than the other machines. Example 2: Same machine as above, except we are running in an environment where many applications are running with inadequate RAM. Also, in this environment, the system is running applications that are started, run, left idle, and not in constant use. A session of FRAME running in a window, for example. What happens is that eventually (theoretically) all applications will be paged out at least once. On the AIX system and the other systems the total paging requirements will be the same (assuming similar malloc algorithm). The major difference is that the AIX system allocated the paging space pages before they were actually needed, and the other systems did not allocate them until they were needed. However, most other systems have an internal variable that gets incremented as virtual memory pages are used. AIX does not do this. This can cause the AIX system to run out of paging space (virtual memory), even though malloc() continues to return memory. This "feature" allows sparse memory segments to work, but requires that all normal users of malloc() (sbrk()) know how much virtual memory will be available (actually impossible), and to handle a paging space low condition. A big problem. There are some pretty obvious pros and cons to both methods of doing Virtual Memory. 2. How much paging space do I need? Concerning the rule of thumb of having 2 times RAM for paging space: this is rather simplistic, as are most rules of thumb. If the machine is in a "persistent storage environment", meaning that they have a few small programs, and lots of data, they may not need even as much as 1 times RAM for paging space. For example, a 1GB database server running on a 6000 with 256MB of RAM, and only running about 50MB of "working" storage does not need 512MB of paging space, or even 256MB. They only need the amount of paging space that will allow all their working storage to be paged out to disk. This is because the 1GB database is mostly "persistent storage", and will require little or no paging space. Excessive paging space may simply mean wasted disk space. However, avoid insufficient paging space. Tip: Don't have more than one paging space per disk. Tip: Put lots of RAM in your system - it will use it. 3. Why does vmstat show no free RAM pages? AIX uses RAM as a possibly huge disk buffer. If you read a file in the morning, that file is read into RAM, and left there. If no other programs need that RAM, that file will be left in RAM until the machine is halted. This means that if you need the file again, access will be quick. If you need that RAM, the system will simply use the pages the file was using. The pages were flushed back to disk earlier. This means that you can get a huge speedup in disk access if you have enough RAM. For example, a 200MB database will just ease into RAM if you have a 256MB system. 4. Since vmstat shows no free RAM pages, am I out of RAM? Probably not. Since disk files will be "mapped" into RAM, if vmstat shows lots of RAM pages FREE, then you probably have too much RAM (not usual on a RISC System/6000)! 5. Shouldn't the "avm" and the "fre" fields from vmstat add up to something? No. The "avm" field tells you how much "Active Virtual Memory" AIX thinks you are using. This will closely match the amount of paging space you are using. This number has *ABSOLUTELY* nothing to do with the amount of RAM you are using, and does *NOT* include your mapped files (disk files). 6. Why does the "fre" field from vmstat sometimes show lots of free RAM pages? This will happen after an application that used a lot of RAM via "working" storage (not NFS storage, and not disk file or "persistent" storage) exits. When RAM pages that were used by working storage (a program's stack and data area) are no longer needed, there is no need to leave them around. AIX completely frees these RAM pages. The time to access these pages versus a RAM page holding a "sync'd" mapped file is almost identical. Therefore, there is no need to periodically "flush" RAM. 7. Is the vmstat "fre" field useful? The vmstat "fre" field represents the number of free page frames. If the number is consistently small (less than 500 pages), this is normal. If the number is consistently large (greater than 4000 pages), then you have more memory than you need in this machine. 1.301: How much should I trust the ps memory reports? From: chukran@austin.VNET.IBM.COM Using "ps vg" gives a per process tally of memory usage for each running process. Several fields give memory usage in different units, but these numbers do not tell the whole story on where all the memory goes. First of all, the man page for ps does not give an accurate description of the memory related fields. Here is a better description: RSS - This tells how much RAM resident memory is currently being used for the text and data segments for a particular process in units of kilobytes. (this value will always be a multiple of 4 since memory is allocated in 4 KB pages). %MEM - This is the fraction of RSS divided by the total size of RAM for a particular process. Since RSS is some subset of the total resident memory usage for a process, the %MEM value will also be lower than actual. TRS - This tells how much RAM resident memory is currently being used for the text segment for a particular process in units of kilobytes. This will always be less than or equal to RSS. SIZE - This tells how much paging space is allocated for this process for the text and data segments in units of kilobytes. If the executable file is on a local filesystem, the page space usage for text is zero. If the executable is on an NFS filesystem, the page space usage will be nonzero. This number may be greater than RSS, or it may not, depending on how much of the process is paged in. The reason RSS can be larger is that RSS counts text whereas SIZE does not. TSIZ - This field is absolutely bogus because it is not a multiple of 4 and does not correlate to any of the other fields. These fields only report on a process text and data segments. Segment size which cannot be interrogated at this time are: Text portion of shared libraries (segment 13) Files that are in use. Open files are cached in memory as individual segments. The traditional kernel cache buffer scheme is not used in AIX 3. Shared data segments created with shmat. Kernel segments such as kernel segment 0, kernel extension segments, and virtual memory management segments. Speaking of kernel segments, the %MEM and RSS report for process zero are totally bogus for AIX 3.1. The reason why RSS is so big is that the kernel segment zero is counted twice. For AIX 3.2, this has been changed, but the whole story is still not known. The RSS value for process 0 will report a very small number of the swapper private data segment. It does not report the size of the kernel segment 0, where the swapper code lives. In summary, ps is not a very good tool to measure system memory usage. It can give you some idea where some of the memory goes, but it leaves too many questions unanswered about the total usage. ______________________________________________________________________________ 1.400: How do I make an informative prompt in the shell? In the Korn Shell (ksh), the PS1 variable is expanded each time it is printed, so you can use: $ myhost=`hostname` $ PS1='$LOGNAME@$myhost $PWD \$ ' to get, e.g. bengsig@ieibm1 /u/bengsig $ In the C-shell, use: % set myhost=`hostname` % alias cd 'chdir \!* > /dev/null; set prompt="$LOGNAME@$myhost $cwd % "' % cd to get, e.g. bengsig@dkunix9 /u/bengsig/aixfaq % There is no easy solution in the Bourne Shell. Use the Korn Shell instead. 1.401: How do I set up ksh for emacs mode command line editing? From: scotte@cdsac.uucp (L. Scott Emmons) The ksh has an undocumented way of binding the arrowkeys to the emacs line editing commands. In your .kshrc, add: alias __A=^P alias __B=^N alias __C=^F alias __D=^B alias __H=^A Note that "^P" (et al) must be the actual control sequence. Type "set -o emacs" or put this line in your .profile. Also, you MUST have PTF U406855 for this to work in AIX 3.2. The APAR # for the problem is IX25982, which may have been superceded. 1.402: Listing files with ls causes a core dump From: John F Haugh II Scenario: a directory that is shared by N users (N >= 200). Run 'ls -l' in that directory. It goes for a while, then Seg fault(coredump)! It only occurs when the usernames are displayed (almost every file is owned by a different person). The -g and -n options work fine; only -l and -o (which shows owner and not group) cause it. I believe that this problem was corrected by U407548. If you have that many users that you are having core dump problems (it took over 200), you might also want to look into getting the PTF that fixes IX31403. That APAR deals with large numbers of accounts and performance problems associated with looking them up. 1.403: How do I put my own text into InfoExplorer? With AIX 3.1, you cannot do it. AIX 3.2 has a product called InfoCrafter that allows you to do that. 1.404: InfoExplorer ASCII key bindings From: mycroft@hal.gnu.ai.mit.edu (Charles Hannum) If you just press 'Return' when it starts up, with 'Basic Screen Operations' highlighted, you'll get some help. If you look long enough, you'll find a page named 'Using Keys and Key Sequences in the InfoExplorer ASCII Interface'. It describes the key sequences and actions. Here are a few to get you started. Keys Action Ctrl-W Moves between the Navigation screen and the Reading screen. If the Navigation screen is displayed, you can press Ctrl-W to display the Reading screen. If the Reading screen is displayed, you can press Ctrl-W to display the Navigation screen. Ctrl-O Makes the menu bar active or inactive. If your text cursor is located in the text area of the screen, you can press Ctrl-O to make the menu bar active. If the menu bar is already active, you can press Ctrl-O to make it inactive, which moves the text cursor to the text area. Tab Moves to the next menu bar option in the menu bar. If a pull-down menu is not displayed and you press the Right Arrow key, the next menu bar option is displayed in reverse video. 1.405: How can I add new man pages to the system? From: horst@faui63.informatik.uni-erlangen.de (Horst Luehrsen) Put the man pages in /usr/man, e.g. /usr/man/man1/tcsh.1 for the tcsh man page. Unter AIX 3.1.10, /usr/lib/makewhatis can be used to update the makewhatis-database /usr/man/whatis so apropos and whatis know about the added manpages. /usr/lib/makewhatis should be available on all 3.2 versions. ______________________________________________________________________________ 1.500 Which release of X11 do I have? Run 'lslpp -h X11rte.obj'. If your output has a line similar to: 01.02.0000.0000 COMPLETE COMMIT 03/04/93 02:05:11 root you have X11 R4. If your output has a line similar to: U491068 01.02.0003.0000 COMPLETE COMMIT 07/28/93 12:50:42 root you have X11 R5. Some people also call these AIXwindows 1.2.0 and 1.2.3. 1.501: How to prevent ctrl-alt-backspace from killing the X session Start X with 'xinit -T' to disable ctrl-alt-backspace from stopping X. 1.502: Who has a termcap/terminfo source for the HFT console? The console used on the RISC System/6000, PS/2 and RT can be used as a terminal on another system with the termcap below. You can find this and other termcaps in /lib/libtermcap/termcap.src, including IBM specific ones. The terminfo sources are stored in /usr/lib/terminfo/*.ti. This termcap can also be used from an aixterm window. hf|hft|hft-c|ibm8512|ibm8513|IBM_High_Function_Terminal:\ :co#80:li#25:am:ht:\ :cm=\E[%i%d;%dH:ti=\E[25;1H:te=\E[20h:\ :nd=\E[C:up=\E[A:do=^J:ho=\E[H:\ :bs:sf=\E[S:ec=\E[%dX:\ :cl=\E[H\E[J:cd=\E[J:ce=\E[K:\ :AL=\E[%dL:DL=\E[%dM:al=\E[L:dl=\E[M:\ :im=\E[4h:ei=\E[4l:mi:\ :dm=\E[4h:ed=\E[4l:\ :so=\E[7m:se=\E[m:ul=\E[4m:ue=\E[m:\ :md=\E[1m:mr=\E[7m:mb=\E[5m:me=\E[m:\ :as=^N:ae=^O:sc=\E[s:rc=\E[u:\ :kl=\E[D:kb=^H:kr=\E[C:ku=\E[A:kd=\E[B:kh=\E[H:\ :kn#10:k1=\E[001q:k2=\E[002q:k3=\E[003q:k4=\E[004q:k5=\E[005q:\ :k6=\E[006q:k7=\E[007q:k8=\E[008q:k9=\E[009q:k0=\E[010q:\ :is=\Eb\E[m^O\E[?7h:rs=\Eb\E[m^O\E[?7h\E[H\E[J: 1.503: How can I look at PostScript files? Why is "dpsexec" so lousy? From: VRBASS@ATLVMIC1 (Vance R. Bass) You can look at PostScript files using either "xpreview" (in the optionally installable text formatting services) or you can get Ghostscript and Ghostview from a comp.sources.x server and build it yourself. >From the "xpreview" man page: The xpreview command is an AIXwindows 1.2- and Motif 1.1-based application that displays output from the troff command on an AIXwindows display. The troff command output file must be prepared for any one of the devX100, devX100K or devpsc devices. The xpreview command also displays PostScript language files that begin with %!. "dpsexec" is NOT intended to be a full-service document browser, but rather a simple DPS code debugger. If you insist on using it, you can edit your PS code to remove the "showpage" (which will reset dpsexec and clear the window) to view single-page files. It does not handle multi-page files gracefully. 1.504: unix:0 vs `hostname`:0 1.) Is there any way to get the machine to check its local host table first without renaming resolv.conf? From: mcguire@selway.umt.edu (Charles J McGuire) Not that I know of. Under SunOS and Ultrix you can specify, check /etc/hosts, then NIS, then DNS. On our AIX machines, I have a cron job that checks the integrity of both the primary and secondary nameservers every 5 minutes. If they're gone, cron renames resolv.conf. It continues to check the servers. When they're back, it moves resolv.conf back. Even with this arrangement, I need to configure two resolv.conf files that switch the order of the primary and secondary servers if the primary goes away. If the primary is unavailable, queries can still take a while to time out on the primary, before querying the secondary. This method is not very elegant, but it does the job. Things are a little unstable during the transitions depending on when the servers go away relative to when cron runs - not to mention slight differences in clock times. 2.) How do you tell X applications where you are if the console display is unix:0? From: crow@waterloo.austin.ibm.com (David L. Crow) I would suggest that if you have R5, use ":<display>.<screen>". I do not believe that R4 clients will understand :0, so I would suggest unix:0 for them. Without specifying unix or the hostname, you will get the fastest transport mechanism. While currently there are only two transport methods in the AIXwindows X server (Unix sockets and TCP sockets), many vendors are looking at using shared memory as a transport method. If you use :0 (or :0.0 or :1, etc.), then you should get the best performance regardless of the available transport methods. 3.) Is there a significant performance penalty incurred by using `hostname`:0 as DISPLAY? Yes! Using unix:0, you are using Unix sockets. These are much faster than their TCP socket counterparts. 1.505: VT100 key bindings for aixterm From: haedener@iac.unibe.ch (Konrad Haedener) Add this to your .Xdefaults file and start your VAX session with 'aixterm -v -name vt100 -e telnet MYVAXHOST' ----- vt100.foreground: Wheat vt100.background: MidnightBlue vt100.font: Rom14.500 vt100.geometry: 80x25+0+0 vt100.vt102: true vt100.fullcursor: false vt100.pointerColor: coral vt100.cursorColor: gray100 vt100.translations: <Key>F1: string(0x1b) string("OP") \n\ <Key>F2: string(0x1b) string("OQ") \n\ <Key>F3: string(0x1b) string("OR") \n\ <Key>F4: string(0x1b) string("OS") \n\ <Key>KP_0: string(0x1b) string("Op") \n\ <Key>KP_1: string(0x1b) string("Oq") \n\ <Key>KP_2: string(0x1b) string("Or") \n\ <Key>KP_3: string(0x1b) string("Os") \n\ <Key>KP_4: string(0x1b) string("Ot") \n\ <Key>KP_5: string(0x1b) string("Ou") \n\ <Key>KP_6: string(0x1b) string("Ov") \n\ <Key>KP_7: string(0x1b) string("Ow") \n\ <Key>KP_8: string(0x1b) string("Ox") \n\ <Key>KP_9: string(0x1b) string("Oy") \n\ <Key>KP_Divide: string(0x1b) string("OQ") \n\ <Key>KP_Multiply: string(0x1b) string("OR") \n\ <Key>KP_Subtract: string(0x1b) string("OS") \n\ <Key>KP_Add: string(0x1b) string("Om") \n\ <Key>KP_Enter: string(0x1b) string("OM") \n\ <Key>KP_Decimal: string(0x1b) string("On") \n\ <Key>Next: string(0x1b) string("Ol") \n\ <Key>Left: string(0x1b) string("OD") \n\ <Key>Up: string(0x1b) string("OA") \n\ <Key>Right: string(0x1b) string("OC") \n\ <Key>BackSpace : string(0x7f) \n\ <Key>Down: string(0x1b) string("OB") You should also add XENVIRONMENT=$HOME/.Xdefaults export XENVIRONMENT to your .profile. ______________________________________________________________________________ 1.600: My named dies frequently, why? Running on 3.2, named dies frequently on network's primary name server. From: jpe@ee.egr.duke.edu (John P. Eisenmenger) Try the following: stopsrc -s named # stop running named setenv MALLOCTYPE 3.1 # use 3.1 memory allocation algorithm /etc/named ... # don't use smit to start named You might be able to use startsrc/smit after setting MALLOCTYPE and get the same effect, but I'm not sure. [According to John, the problem is malloc() in the named code. He also suggests using Berkeley's bind, which he has ported and can be ftp'ed from ftp.egr.duke.edu, /archives/network/bind-4.8.3.tar.Z. -ed] Two ptfs should fix this problem. Get U412332 and U414752. Christophe Wolfhugel <Christophe.Wolfhugel@grasp.insa-lyon.fr> reports that bind 4.9 works fine on AIX 3.2 and without MALLOCTYPE=3.1. 1.601: How do I trace ethernet packets on an AIX system? From: afx@muc.ibm.de (Andreas Siegert) Do the following: iptrace -i en0 /tmp/ipt The iptrace backgrounds. Find its process id and kill it when you are ready. Then run ipreport -rns /tmp/ipt >/tmp/ipr and look at the output. The current version of Info does not document the r, n and s options but they are quite useful for layering the output. 1.602 What is the authorized way of starting automount at boot time? From: curt@ekhadafi.austin.ibm.com (Curt Finch) I put this in my /etc/inittab: automount:2:once:/usr/etc/automount -T -T -T -v >/tmp/au.se 2>&1 I hereby dub it authorized. 1.603: How do I set a tty port for both dial-in and dial-out? Set the mode of the tty to be either 'shared' or 'delayed'. 1.604: How to move or copy whole directory trees across a network The following command will move an entire directory tree across a network while preserving permissions, uids and gids. $rsh RemoteHost "cd TargetDir; tar -cBf - ." | tar -xvBf - Explanation: The tar-create is rsh'd to the remote system and is written to stdout (the pipe). The local system is extracting the tar that is being read from stdin (the pipe). 1.605: How can I send mail to hosts that cannot be pinged? From: jupiter.sun.csd.unb.ca!dedourek (John DeDourek) AIX 3.2 as shipped is configured to only send mail to mail addresses which include a host name. Many organizations use a mail address whose "host name" part is not a host name (technically an MX name). To change the configuration of the AIX mailer, login as root. Then edit the file /etc/sendmail.cf to remove the comment marker ("# ") at the beginning of the line which reads: # OK MX Now rebuild the machine readable form of the configuration with sendmail -bz and finally restart signal sendmail to load the new configuration by one of the following: reboot or stopsrc -s sendmail startsrc -s sendmail or kill -1 `cat /etc/sendmail.pid` 1.606: How to setup dialup SLIP From: marvin@tornado.oche.de (Christian Bode) If you don't have problems with slattach you should have PTF bos.obj 3.2.0.0.U411505 installed. I assume that you did the right ifconfig commands to setup your slip-device (for example sl0). 1. Create a group called slip. 2. Create a user slip with smit like this: [Entry Fields] * User NAME [slip] ADMINISTRATIVE User? true User ID [] LOGIN user? true PRIMARY group [slip] Group SET [slip] ADMINISTRATIVE groups [system] SU groups [slip] HOME directory [/home/slip] Initial PROGRAM [/bin/sh] User INFORMATION [SLIP-Dialup] Another user can SU to user? false User can RLOGIN? true TRUSTED PATH? nosak Valid TTYs [/dev/tty1] AUDIT classes [] PRIMARY authentication method [SYSTEM] SECONDARY authentication method [NONE] Max FILE size [2097151] Max CPU time [-1] Max DATA segment [262144] Max STACK size [65536] Max CORE file size [2048] Max physical MEMORY [65536] File creation UMASK [022] EXPIRATION date (MMDDhhmmyy) [0] 3. Create a tty with getty on it: Add a TTY [Entry Fields] TTY type tty TTY interface rs232 Description Asynchronous Terminal Parent adapter sa0 * PORT number [s1] BAUD rate [38400] PARITY [none] BITS per character [8] Number of STOP BITS [1] TERMINAL type [dumb] STATE to be configured at boot time [available] DMA on Read Trigger 0,1,2,3 Transmit buffer count [16] Name of initial program to run [/etc/getty] Note: The following attributes are only applicable if /etc/getty is specified as the initial program to run. Enable program? respawn Run level 2 Enable LOGIN share TIME before advancing to next port setting [0] STTY attributes for RUN TIME [hupcl,cread,brkint> STTY attributes for LOGIN [hupcl,cread,echoe,> RUN shell activity manager no Optional LOGGER name [] 4. Change the hardware characteristics so that it uses NO XON/XOFF handshake 5. Here is the the .profile for User slip to manage dialups PATH=/usr/bin:/etc:/usr/sbin:/usr/ucb:$HOME/bin:/usr/bin/X11:/sbin:/usr/local/bin:. ENV=$HOME/.kshrc HISTSIZE=128 export PATH ENV HISTSIZE # # Search for a LCK-File for our tty if there is one # if test -f /etc/locks/LCK..tty1 then SHPID=`cat /etc/locks/LCK..tty1` else echo `date` " No LCK-File !!!" >>slip.log exit 64 fi # # Search for our own Shell to get the PID for checking against LCK-File # SH2PID=`ps -aef | sed -n -e 's/^ *slip *$[0-9][0-9]*$ .*-sh *$/\1/p` # # Is it the the same PID as in the LCK File so that we can start working ?? # if test $SHPID = $SH2PID then # remove the LCK-File because slattach does not like it. rm -rf /etc/locks/LCK..tty1 # Add RTS/CTS Handshakeing to our own tty stty add rts # Startup slattach. Slattach has to have mode 4755 to be started up !!! /usr/sbin/slattach tty1 # Just say that we are up. echo `date` " Starting up slip-daemon " >>slip.log # leave slattach enough time to startup sleep 4 else # Something must be wrong with the LCK-File SH3PID=`ps -aef | awk ' {print $2}' | grep $SHPID` if test ."$SH3PID" = ."" then SH3PID="NO_SUCH_PROCESS" fi if test $SHPID = $SH3PID then # There is a living process which owns the LCK-File !! echo `date` " Can't remove LCK-File, not owner !!!" >>slip.log exit 64 else # Who the hell didn't remove the LCK-File (should never happen) echo `date` " LCK-File with no owner found !!!" >>slip.log exit 64 fi fi # Get the pid of slattch so that we can kill him later on. SLPID=`ps -aef | sed -n -e 's/^ *slip *$[0-9][0-9]*$ .*-.*\/usr\/sbin\/slattach tty1 *$/\1/p` # Kill slattach if we get a signal 1 (Carrier Lost ? / Otherside-slattach terminated ) trap "kill $SLPID; exit 0" 1 # We will have a nice sleep and nice dreamings while sleep 256 do : done 1.607: Where is DCE discussed? From: brent@uwovax.uwo.ca (Brent Sterner) DCE is the Distributed Computing Environment, which is roughly a flexible client-server architecture for heterogenous platforms. For more information, take a look in comp.unix.osf.misc. 1.608: How do I make /var/spool/mail mountable? From: petersen@pi1.physik.uni-stuttgart.de (Joerg Petersen) In our cluster we share a /usr/local disk. We have a directory /usr/local/spool/mail and /var/spool/mail is soft-linked to it. From: fred@hal6000.thp.Uni-Duisburg.DE (Fred Hucht) Several problems has been reported on sharing the mail directory via NFS. The problems may occur when two or more sendmail daemons and/or mail readers access a user's mail file simultanously, because of NFS' file locking mechanism. We use another method here: Every user has one line in his/her $HOME/.forward file that reads xxx@mainserver.domain.name where xxx is the user node and mainserver.domain.name is the full hostname of one of the machines. Then all incoming mail to all machines is forwarded to mainserver, while mainserver ignores this line. ______________________________________________________________________________ 1.900: SCSI-1 and SCSI-2 "interoperability" got you confused? From: drr A. SCSI-1 devices are supported on a SCSI-2 adapter. This config will provide SCSI-1 performance. B. SCSI-2 devices are supported on a SCSI-1 adapter. This config will provide SCSI-1 performance. C. A mix of SCSI-2 and SCSI-1 devices are supported on a SCSI-1 adapter. All devices will have SCSI-1 performance. D. A mix of SCSI-2 and SCSI-1 devices are supported on a SCSI-2 adapter. SCSI-2 devices will have SCSI-2 performance (10 MB/sec) and SCSI-1 devices will have SCSI-1 performance (4-5 MB/sec). 1.901: How to get your keyboard back after unplugging it from the 6000 From: Mickey Coggins and Anne Serre When you unplug your keyboard from a running system, and plug it back in, the key mapping is wrong. For example, keys like Caps Lock and Ctrl don't work as designed. Solution: Type at the command line /usr/lpp/diagnostics/da/dkbd Your screen goes black, you hear a few beeps, and your keyboard is reset. It works with any environment, Xwindows, hft, NLS... For Models 220, 230 and M20, use the following commands: /usr/lpp/diagnostics/da/dkbd /usr/lpp/diagnostics/da/dkbdsal (for the 220) 1.902: How do I set up pcsim, the DOS emulator? You must have a bootable DOS diskette to install pcsim. Either DOS 3.3, 4.x, or 5.0 will work. IBM do not officially support DOS 5.0 for pcsim but I have no problems with it. Just don't try to be fancy with the UMB and memory manager stuff. With a bootable DOS disk in the drive, do: $touch /u/dosdrive (this is the AIX file for DOS emulation) $pcsim -Adiskette 3 -Cdrive /u/dosdrive You would now get an A prompt. Type: A> fdisk Create the virtual C drive of whatever size you choose. Make it large enough for your needs since you cannot enlarge it later. A> format c: /s (to format the virtual C drive) Now exit from pcsim with ESCpcsim (Esc key followed by pcsim). Now create a simprof file. Following is a starter: Adiskette : 3 Cdrive :/u/dosdrive lpt1 : name of printer queue refresh : 50 dmode : V mouse : com1 You can now start pcsim anytime by typing pcsim. Make sure no floppies are in the drive. For further information, refer to publication SC23-2452, Personal Computer Simulator/6000 Guide and Reference. 1.903: How do I transfer files between AIX and DOS disks? In one of the bos extensions are commands for transferring files between DOS diskettes and AIX. The commands are dosread, doswrite, dosdir, dosdel, and dosformat. Many users have mentioned that the mtools package from prep.ai.mit.edu is better than the native AIX programs. _____________________________________________________________________________ 2.00: C/C++ Contrary to many people's belief, the C environment on the RS/6000 is not very special. The C compiler has quite a number of options that can be used to control how it works, which "dialect" of C it compiles, how it interprets certain language constructs, etc. InfoExplorer includes a Users Guide and a Reference Manual. The compiler can be invoked with either xlc for strict ANSI mode and cc for RT compatible mode (i.e. IBM 6150 with AIX 2). The default options for each mode are set in the /etc/xlc.cfg file, and you can actually add another stanza and create a link to the /bin/xlc executable. The file /usr/lpp/xlc/bin/README.xlc has information about the C compiler, and the file /usr/lpp/bos/bsdport contains useful information, in particular for users from a BSD background. The file /etc/xlc.cfg also shows the symbol _IBMR2 that is predefined, and therefore can be used for #ifdef'ing RS/6000 specific code. 2.01: I cannot make alloca work A famous routine, in particular in GNU context, is the allocation routine alloca(). Alloca allocates memory in such a way that it is automatically free'd when the block is exited. Most implementations does this by adjusting the stack pointer. Since not all C environments can support it, its use is discouraged, but it is included in the xlc compiler. In order to make the compiler aware that you intend to use alloca, you must put the line #pragma alloca before any other statements in the C source module(s) where alloca is called. If you don't do this, xlc will not recognize alloca as anything special, and you will get errors during linking. For AIX 3.2, it may be easier to use the -ma flag. 2.02: How do I compile my BSD programs? The file /usr/lpp/bos/bsdport contains information on how to port programs written for BSD to AIX 3.1. This file may be very useful for others as well. A quick cc command for most "standard" BSD programs is: $ cc -D_BSD -D_BSD_INCLUDES -o [loadfile] [sourcefile.c] -lbsd If your software has system calls predefined with no prototype parameters, also use the -D_NO_PROTO flag. 2.03: Isn't the linker different from what I am used to? Yes. It is not at all like what you are used to: - The order of objects and libraries is normally _not_ important. The linker reads _all_ objects including those from libraries into memory and does the actual linking in one go. Even if you need to put a library of your own twice on the ld command line on other systems, it is not needed on the RS/6000 - doing so will even make your linking slower. - One of the features of the linker is that it will replace an object in an executable with a new version of the same object: $ cc -o prog prog1.o prog2.o prog3.o # make prog $ cc -c prog2.c # recompile prog2.c $ cc -o prog.new prog2.o prog # make prog.new from prog # by replacing prog2.o - The standard C library /lib/libc.a is linked shared, which means that the actual code is not linked into your program, but is loaded only once and linked dynamically during loading of your program. - The ld program actually calls the binder in /usr/lib/bind, and you can give ld special options to get details about the invocation of the binder. These are found on the ld man page or in InfoExplorer. - If your program normally links using a number of libraries (.a files), you can 'prelink' each of these into an object, which will make your final linking faster. E.g. do: $ cc -c prog1.c prog2.c prog3.c $ ar cv libprog.a prog1.o prog2.o prog3.o $ ld -r -o libprog.o libprog.a $ cc -o someprog someprog.c libprog.o This will solve all internal references between prog1.o, prog2.o and prog3.o and save this in libprog.o Then using libprog.o to link your program instead of libprog.a will increase linking speed, and even if someprog.c only uses, say prog1.o and prog2.o, only those two modules will be in your final program. This is also due to the fact that the binder can handle single objects inside one object module as noted above. If you are using an -lprog option (for libprog.a) above, and still want to be able to do so, you should name the prelinked object with a standard library name, e.g. libprogP.a (P identifying a prelinked object), that can be specified by -lprogP. You cannot use the archiver (ar) on such an object. You should also have a look at section 3.01 of this article, in particular if you have mixed Fortran/C programs. Dave Dennerline (dad@adonis.az05.bull.com) claims that his experiences in prelinking on AIX does not save much time since most people have separate libraries which do not have many dependencies between them, thus not many symbols to resolve. 2.04: How do I link my program with a non-shared /lib/libc.a? cc -o prog -bnoso -bI:/lib/syscalls.exp obj1.o obj2.o obj3.o will do that for a program consisting of the three objects obj1.o, etc. 2.05: How do I make my own shared library? To make your own shared object or library of shared objects, you should know that a shared object cannot have undefined symbols. Thus, if your code uses any externals from /lib/libc.a, the latter MUST be linked with your code to make a shared object. Mike Heath (mike@pencom.com) said it is possible to split code into more than one shared object when externals in one object refer to another one. You must be very good at import/export files. Perhaps he or someone can provide an example. Assume you have one file, sub1.c, containing a routine with no external references, and another one, sub2.c, calling stuff in /lib/libc.a. You will also need two export files, sub1.exp, sub2.exp. Read the example below together with the examples on the ld man page. ---- sub1.c ---- int addint(int a, int b) { return a + b; } ---- sub2.c ---- #include <stdio.h> void printint(int a) { printf("The integer is: %d\n", a); } ---- sub1.exp ---- #! addint ---- sub2.exp ---- #! printint ---- usesub.c ---- main() { printint( addint(5,8) ); } The following commands will build your libshr.a, and compile/link the program usesub to use it. Note that you need the ld option -lc for sub2shr.o since it calls printf from /lib/libc.a. $ cc -c sub1.c $ ld -o sub1shr.o sub1.o -bE:sub1.exp -bM:SRE -T512 -H512 $ cc -c sub2.c $ ld -o sub2shr.o sub2.o -bE:sub2.exp -bM:SRE -T512 -H512 -lc $ ar r libshr.a sub1shr.o sub2shr.o $ cc -o usesub usesub.c -L: libshr.a $ usesub The integer is: 13 $