OpenBSD FAQ - System Management [FAQ Index]

• Security updates
• System daemons
• Executing commands as another user
• Editing the password file
• Using S/Key
• Directory services
  • Which directory services are available?
  • YP security considerations
  • Setting up a YP server
  • Setting up a YP client

Security updates

For the OpenBSD base system, there are four options:

• Apply binary patches
  If you're running the -release branch of OpenBSD, you can simply use the syspatch(8) utility to upgrade any files in need of security or reliability fixes. This is the quickest and easiest method to get the base system up to date. Note that binary patches are only available for the amd64 and i386 architectures.
• Update your system to -stable
  Fetch (or update) your source tree with CVS, then recompile the kernel and userland.
• Patch the affected files individually
  While applying fixes from the errata page typically requires less time than a CVS checkout/update and rebuild, there is no universal set of instructions to follow. Sometimes you must patch and recompile one application, sometimes more.
• Upgrade your system to -current
  As all fixes are applied to the -current code base, updating your system to the latest snapshot is a good way to get all the fixes at once. However, running -current is not for everyone.

• Upgrade your system to -current and use binary packages
  Binary packages for -current snapshots are rebuilt on a regular basis, and these new packages will include any security fixes that were committed. Simply call pkg_add(1) with the -u flag after picking a mirror to get the new files.
• Use the -stable ports tree
  Fetch (or update) your ports tree with CVS, run the /usr/ports/infrastructure/bin/out-of-date script to list any packages that need rebuilding, and issue make update in the affected port directory. Alternatively, packages can be built in bulk with dpb(1). To be alerted of port updates, consider following the "ports-changes" mailing list.

System daemons

Most daemons and services that come with OpenBSD are controlled on boot by variables defined in /etc/rc.conf. You'll see lines similar to this:

httpd_flags=NO

Do not alter rc.conf(8) directly. Instead, use the rcctl(8) utility to maintain the /etc/rc.conf.local file. This makes future upgrades easier -- all the changes are in the one file that isn't touched during upgrade.

For example, to start the apmd(8) daemon for CPU scaling, you might do:

# rcctl enable apmd
# rcctl set apmd flags -A
# rcctl start apmd

Executing commands as another user

For example, if appropriately configured, the following command would display root's crontab(5) file:

$ doas crontab -l -u root

Editing the password file

Always use vipw(8) to edit your /etc/master.passwd file. vipw(8) will invoke your $EDITOR to edit a copy of /etc/master.passwd. After you are done editing, vipw(8) will first sanity check your changes, then it will re-create /etc/passwd and the password databases, and finally it will install the copy in place of the original /etc/master.passwd file. vipw(8) also takes care of locking these files, so that only one user can make changes at a time.

Using S/Key

WARNING: One-time password systems only protect authentication information. They do not prevent network eavesdroppers from gaining access to private information. Furthermore, if you are accessing a secure system A, it is recommended that you do this from another trusted system B, to ensure nobody is gaining access to system A by logging your keystrokes or by capturing and/or forging input and output on your terminal devices.

Setting up S/Key

# skeyinit -E

$ skeyinit
Reminder - Only use this method if you are directly connected
           or have an encrypted channel.  If you are using telnet,
           exit with no password and use skeyinit -s.
Password:
[Adding ericj with md5]
Enter new secret passphrase:
Again secret passphrase:

ID ericj skey is otp-md5 100 oshi45820
Next login password: HAUL BUS JAKE DING HOT HOG

Generating S/Key passwords

$ skeyinfo -v
otp-md5 95 oshi45820
$ otp-md5 95 oshi45820
Reminder - Do not use this program while logged in via telnet.
Enter secret passphrase:
NOOK CHUB HOYT SAC DOLE FUME

$ otp-md5 -n 5 95 oshi45820
Reminder - Do not use this program while logged in via telnet.
Enter secret passphrase:
91: SHIM SET LEST HANS SMUG BOOT
92: SUE ARTY YAW SEED KURD BAND
93: JOEY SOOT PHI KYLE CURT REEK
94: WIRE BOGY MESS JUDE RUNT ADD
95: NOOK CHUB HOYT SAC DOLE FUME

Using S/Key to log in

$ ftp localhost
Connected to localhost.
220 oshibana.shin.ms FTP server (Version 6.5/OpenBSD) ready.
Name (localhost:ericj): ericj:skey
331- otp-md5 93 oshi45820
331 S/Key Password: JOEY SOOT PHI KYLE CURT REEK
[...]
230 User ericj logged in.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> quit
221 Goodbye.

$ ssh -l ericj:skey localhost
otp-md5 91 oshi45821
S/Key Password: SHIM SET LEST HANS SMUG BOOT
Last login: Thu Apr  7 12:21:48 on ttyp1 from 156.63.248.77
$

Directory services

Which directory services are available?

YP is a directory service compatible with Sun Microsystems NIS (Network Information System). See yp(8) for an overview of the available manual pages. Be careful, some operating systems contain directory services bearing similar names but all the same being incompatible, for example NIS+.

To use directory services other than YP, you either need to populate local configuration files from the directory, or you need a YP frontend to the directory. For example, you can use the sysutils/login_ldap port when you choose the former, while the ypldap(8) daemon provides the latter.

For some applications, simply synchronizing a small number of configuration files among a group of machines using tools like cron(8), scp(1) or rsync (available from ports) constitutes an easy and robust alternative to a full-blown directory service.

YP security considerations

Thus, before setting up any YP server, you should consider whether these inherent security flaws are acceptable in your context. In particular, YP is inadequate if potential attackers have physical access to your network. Anybody gaining root access to any computer connected to your network segments carrying YP traffic can bind your YP domain and retrieve its data. In some cases, passing YP traffic through SSL or IPSec tunnels might be an option.

Setting up a YP server

1. A YP server serves a group of clients called a "domain." You should first select a domain name; it can be an arbitrary string and need not be related in any way to DNS domain names. Choosing a random name like "Eepoo5vi" can marginally improve security, though the effect is mostly in security by obscurity. In case you need to maintain several distinct YP domains, it's probably better to choose descriptive names like "sales," "marketing" and "research" in order to forestall system administration errors caused by obscurity. Also note that some versions of SunOS require using the host's DNS domain name, so your choice might be restricted in a network including such hosts.

   Use the domainname(1) utility to set the domain name, and put it into the defaultdomain(5) file to have it automatically set at system startup time.

       # echo "puffynet" > /etc/defaultdomain
       # domainname `cat /etc/defaultdomain`
       

2. Initialise the YP server using the interactive command

       # ypinit -m
       

   At this point, it is not necessary to specify slave servers yet. To add slave servers, you can rerun ypinit(8) later, using the -u option. Setting up at least one slave server for each domain is useful to avoid service interruptions. For example, should the master server ever go down or lose network connectivity, client processes trying to access YP maps block indefinitely until they receive the requested information. Thus, YP service interruptions typically render the client hosts completely unusable until YP is back to service.
3. Decide where to store the source files to generate your YP maps from. Keeping the server configuration separate from the served configuration helps to control which information will be served and which won't, so the default /etc often isn't the best choice.

   The only inconvenience caused by changing the source directory is that you will not be able to add, remove and modify users and groups in the YP domain using utilities like user(8) and group(8). Instead, you will have to edit the configuration files with a text editor.

   To define the source directory, edit the file /var/yp/`domainname`/Makefile and change the DIR variable, e.g.

       DIR=/etc/yp/src/puffynet
       

4. Consider customizing other variables in /var/yp/`domainname`/Makefile. See Makefile.yp(8) for details.

   For example, even in case you use the default source directory /etc, you do not usually need all accounts and groups existing on the server on all your client hosts. In particular, not serving the root account and thus keeping root's password hash confidential is often beneficial to security. Review the values of MINUID, MAXUID, MINGID and MAXGID and adjust them to you needs.

   If all your YP clients run OpenBSD or FreeBSD, exclude the encrypted passwords from the passwd maps by setting UNSECURE="" in /var/yp/`domainname`/Makefile.

   The former practice of editing the template file /var/yp/Makefile.yp is no longer recommended. Changes to that file affect all domains initialized after the change, but do not affect domains initialized before the change, so this is error-prone either way: You both risk that the intended changes do not take effect, and you risk to forget about them and have them affect other domains later which they were never intended for.

5. Create the source directory and populate it with the configuration files you need. See Makefile.yp(8) to learn which YP maps require which source files. For the format of the individual configuration files, refer to passwd(5), group(5), hosts(5) and so on, and look at the examples in /etc.
6. Create the initial version of your YP maps using the commands

       # cd /var/yp
       # make
       

   Do not worry about error messages from yppush(8) right now. The YP server is not yet running.
7. YP uses rpc(3) (remote procedure calls) to communicate with clients, so it is necessary to enable portmap(8). To do so, use rcctl(8).

       # rcctl enable portmap
       # rcctl start portmap
       

8. Consider using either the securenet(5) or the ypserv.acl(5) security feature of the YP server daemon. But be aware that both of these only provide IP based access control. Thus, they only help as long as potential attackers have neither physical access to the hardware of the network segments carrying your YP traffic nor root access to any host connected to those network segments.
9. Finally, start the YP server daemon:

       # rcctl enable ypserv
       # rcctl start ypserv
       

10. To test the new server, consider making it its own client, following the instructions in the first part of the next section. In case you don't want the server to use its own maps, you can disable the client part after the test with the following commands:

        # rcctl stop ypbind
        # rcctl disable ypbind
        

11. Remember that each time you change a file sourced by a YP map, you must regenerate your YP maps.

        # cd /var/yp
        # make
        

    This updates all database files in /var/yp/`domainname`, with one exception: The file ypservers.db, listing all YP master and slave servers associated with the domain, is created directly from ypinit -m and modified exclusively by ypinit -u. In case you accidentally delete it, run ypinit -u to recreate it from scratch.

Setting up a YP client

1. Like on the server, you must set the domain name and enable the portmapper:

       # echo "puffynet" > /etc/defaultdomain
       # domainname `cat /etc/defaultdomain`
       # rcctl enable portmap
       # rcctl start portmap
       

2. It is recommended to provide a list of YP servers in the configuration file /etc/yp/`domainname`. Otherwise, the YP client daemon will use network broadcasts to find YP servers for its domain. Explicitly specifying the servers is both more robust and marginally less open to attack. If you have not set up any slave servers, just put the host name of the master server into /etc/yp/`domainname`.
3. Enable and start the YP client daemon, ypbind(8).

       # rcctl enable ypbind
       # rcctl start ypbind
       

4. If all went well you should be able to query the YP server using ypcat(1) and see your passwd map returned.

       # ypcat passwd
       bob:*:5001:5000:Bob Nuggets:/home/bob:/usr/local/bin/zsh
       ...
       

   Another useful tool for debugging your YP setup is ypmatch(1).

For a list of standard YP maps and their standard usage, see Makefile.yp(8). The most common use cases include:

• If you want to include all user accounts from the YP domain, append the default YP marker to the master password file and rebuild the password database:

      # echo '+:*::::::::' >> /etc/master.passwd
      # pwd_mkdb -p /etc/master.passwd
      

  For details on selective inclusion and exclusion of user accounts, see passwd(5). To test whether inclusion actually works, use the id(1) utility.
• If you want to include all groups from the YP domain, append the default YP marker to the group file:

      # echo '+:*::' >> /etc/group
      

  For details on selective group inclusion, see group(5).