Updating and Modifying Existing Maps

After you have installed NIS, you might discover that some maps require frequent updating while others never need to change. For example, the passwd.byname map can change frequently on a large company's network, while the auto_master map changes little, if at all.

As mentioned in Default NIS Maps, the default location of the default NIS maps is on the master server in /var/yp/domainname, where domainname is the name of the NIS domain. When you need to update a map, you can use one of two updating procedures, depending on whether or not it is a default map.

• A default map is a map in the default set created by ypinit from the network databases.

• Nondefault maps can be any of the following.

  • Maps included with an application purchased from a vendor

  • Maps created specifically for your site

  • Maps created from a nontext file

The following sections explain how to use various updating tools. In practice, you might decide to only use them if you add nondefault maps or change the set of NIS servers after the system is already up and running.

How to Update Maps Supplied With the Default Set

Use the following procedure for updating maps supplied with the default set.

1. Become a superuser on the master server.

   Always modify NIS maps only on the master server.

2. Edit the source file for the map you want to change, whether that file resides in /etc or in some other directory of your choice.
3. Type the following.

   # cd /var/yp
   # make mapname

   The make command then updates your map according to the changes you made in its corresponding file. It also propagates the changes among the other servers.

Maintaining Updated Maps

The following sections describe additional procedures after you have completed updating maps that are supplied with the default set.

Propagating an NIS Map

After a map is changed, the Makefile uses yppush to propagate a new map to the slave servers (unless NOPUSH is set in the Makefile). It does this by informing the ypserv daemon and sending a map transfer request. The ypserv daemon on the slave then starts a ypxfr process, which in turn contacts the ypxfrd daemon on the master server. Some basic checks are made (for example did the map really change?) and then the map is transferred. ypxfr on the slave then sends a response to the yppush process indicating whether the transfer succeeded.

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Note - The above procedure will not work for newly created maps that do not yet exist on the slave servers. New maps must be sent to the slave servers by running ypxfr on the slaves.

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Occasionally, maps fail to propagate and you must to use ypxfr manually to send new map information. You can choose to use ypxfr in two different ways: periodically through the root crontab file, or interactively on the command line. These approaches are discussed in the following sections.

Using cron for Map Transfers

Maps have different rates of change. For instance, some might not change for months at a time, such as protocols.byname among the default maps and auto_master among the nondefault maps; but passwd.byname can change several times a day. Scheduling map transfer using the crontab command allows you to set specific propagation times for individual maps.

To periodically run ypxfr at a rate appropriate for the map, the root crontab file on each slave server should contain the appropriate ypxfr entries. ypxfr contacts the master server and transfers the map only if the copy on the master server is more recent than the local copy.

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Note - If your master server runs rpc.yppasswdd with the default -m option, then each time someone changes their yp password, the passwd daemon runs make, which rebuilds the passwd maps.

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Using Shell Scripts With cron and ypxfr

As an alternative to creating separate crontab entries for each map, you might prefer to have the root crontab command run a shell script that periodically updates all maps. Sample map-updating shell scripts are n the /usr/lib/netsvc/yp directory. The script names are ypxfr_1perday, ypxfr_1perhour, and ypxfr_2perday. You can modify or replace these shell scripts to fit your site requirements. Example 6-1 shows the default ypxfr_1perday shell script.

Example 6-1 ypxfr_1perday Shell Script

#! /bin/sh
#
# ypxfr_1perday.sh - Do daily yp map check/updates
PATH=/bin:/usr/bin:/usr/lib/netsvc/yp:$PATH
export PATH
# set -xv
ypxfr group.byname
ypxfr group.bygid
ypxfr protocols.byname
ypxfr protocols.bynumber
ypxfr networks.byname
ypxfr networks.byaddr
ypxfr services.byname
ypxfr ypservers

This shell script updates the maps once per day, if the root crontab is executed daily. You can also have scripts that update maps once a week, once a month, once every hour, and so forth, but be aware of the performance degradation implied in frequently propagating the maps.

Run the same shell scripts as root on each slave server configured for the NIS domain. Alter the exact time of execution from one server to another to avoid bogging down the master.

If you want to transfer the map from a particular slave server, use the -h machine option of ypxfr within the shell script. Here is the syntax of the commands you put in the script.

# /usr/lib/netsvc/yp/ypxfr -h machine [ -c ] mapname

Where machine is the name of the server with the maps you want to transfer, and mapname is the name of the requested map. If you use the -h option without specifying a machine, ypxfr tries to get the map from the master server. If ypserv is not running locally at the time ypxfr is executed, you must use the -c flag so that ypxfr does not send a clear current map request to the local ypserver.

You can use the -s domain option to transfer maps from another domain to your local domain. These maps should be the same across domains. For example, two domains might share the same services.byname and services.byaddr maps. Alternatively, you can use rcp, or rdist for more control, to transfer files across domains.

Directly Invoking ypxfr

The second method of invoking ypxfr is to run it as a command. Typically, you do this only in exceptional situations – for example, when setting up a temporary NIS server to create a test environment or when trying to quickly get an NIS server that has been out of service consistent with the other servers.

Logging ypxfr Activity

The transfer attempts and results of ypxfr can be captured in a log file. If a file called /var/yp/ypxfr.log exists, results are appended to it. No attempt to limit the size of the log file is made. To prevent it from growing indefinitely, empty it from time to time by typing the following.

# cd /var/yp
# cp ypxfr.log ypxfr.log.old
# cat /dev/null > /var/yp/ypxfr.log

You can have crontab execute these commands once a week. To turn off logging, remove the log file.

Modifying Default Maps

To update a nondefault map, you must do the following.

1. Create or edit its corresponding text file.

2. Build (or rebuild) the new or updated map. There are two ways to build a map.

   • Use the Makefile. Using the Makefile is the preferred method of building a non-default map. If the map has an entry in the Makefile, run make name where name is the name of map you want to build. If the map does not have a Makefile entry, try to create one following the instructions in Modifying and Using the Makefile.

   • Use the /usr/sbin/makedbm program. makedbm(1M) fully describes this command.

Using makedbm to Modify a Non-Default Map

There are two different methods for using makedbm to modify maps if you do not have an input file:

• Redirect the makedbm -u output to a temporary file, modify the file, then use the modified file as input to makedbm.

• Have the output of makedbm -u operated on within a pipeline that feeds into makedbm. This is appropriate if you can update the disassembled map with either awk, sed, or a cat append.

Creating New Maps from Text Files

Assume that a text file /var/yp/mymap.asc was created with an editor or a shell script on the master. You want to create an NIS map from this file and locate it in the homedomain subdirectory. To do this, type the following on the master server.

# cd /var/yp
# makedbm mymap.asc homedomain/mymap

The mymap map now exists on the master server in the directory homedomain. To distribute the new map to slave servers run ypxfr.

Adding Entries to a File-Based Map

Adding entries to mymap is simple. First, you must modify the text file /var/yp/mymap.asc. If you modify the actual dbm files without modifying the corresponding text file, the modifications are lost. Then run makedbm as shown above.

Creating Maps From Standard Input

When no original text file exists, create the NIS map from the keyboard by typing input to makedbm, as shown below (end with Control-D).

ypmaster# cd /var/yp
ypmaster# makedbm -homedomain-/mymapkey1 value1 key2 value2 key3 value3

Modifying Maps Made From Standard Input

If you later need to modify the map, you can use makedbm to disassemble the map and create a temporary text intermediate file. To disassemble the map and create a temporary file, type the following.

% cd /var/yp
% makedbm -u homedomain/mymap > mymap.temp

The resulting temporary file mymap.temp has one entry per line. You can edit this file as needed, using any text editor.

To update the map, give the name of the modified temporary file to makedbm by typing the following.

% makedbm mymap.temp homedomain/mymap
% rm mymap.temp

Then propagate the map to the slave servers, by becoming root and typing the following.

# yppush mymap

The preceding paragraphs explained how to use makedbm to create maps; however, almost everything you actually have to do can be done by ypinit and Makefile unless you add nondefault maps to the database or change the set of NIS servers after the system is already up and running.

Whether you use the Makefile in /var/yp or some other procedure the goal is the same. Anew pair of well-formed dbm files must end up in the maps directory on the master server.