debian-dns 2014 Davor Ocelic Davor Ocelic docelic@spinlocksolutions.com SPINLOCK— advanced GNU/Linux and Unix solutions for commercial and education sectors. Last update: Jan 12, 2014. — Initial version This documentation is free; you can redistribute it and/or modify it under the terms of the &GNU; General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. The purpose of this article is to give you a straight-forward, Debian/Ubuntu-friendly way of installing and configuring ISC BIND 9. This is not a thorough guide on DNS or BIND 9. It's primary purpose is to serve as a supporting document to the &SL;'s practical 4-piece introductory series to infrastructure-based Unix networks, containing &DKLAR_DEB;, &DKLAR_KRB;, &DKLAR_LDA; and &DKLAR_AFS;. As such, it should be read first as all other documents depend on a functional DNS setup.

ISC BIND is a service that has been traditionally captivating system administrators' and advanced users' interest, but its (seemingly or not) high entry barrier and infrastructure requirements have been preventing many from using it. BIND 9 has already been the topic of numerous publications. Here, we will present only the necessary summary; enough information to establish the context and to achieve practical results. You do not need to follow any external links; however, the links have been provided both throughout the article and listed all together at the end, to serve as pointers to more precise technical treatment of individual topics.

DNS is intended to centrally resolve hostnames to IP addresses within a local network as well as on the Internet. In addition to performing basic name resolution for hosts and e-mail servers, DNS can also contain other service-specific records allowing infrastructural services, such as &KRB;, &LDA; and &AFS; to perform a lot of service configuration discovery through DNS. Historically, DNS has not been part of this introductory documentation series to infrastructure-based Unix networks. However, this has resulted in the documents using sub-optimal name resolution schemes, as well as showing suboptimal setups, requiring readers to perform additional configuration before they could consider their setups officially sound. This document aims to improve that area and allow one to set up a solid infrastructure from the ground up. ... More description on what exactly DNS will do ... While the idea of a network name resolution is not unique, let's quickly identify the specific name resolution elements in our setup: Our DNS server will be used to resolve hostnames on the local network while the requests for outside hostnames will be forwarded to the Internet DNS servers. The hosts on the local network will all be using the local DNS server for name resolution, counting that their requests for Internet hostnames will be forwarded to the appropriate DNS servers. You can find the complete DNS documentation at the &BIN; website.

On all GNU/Linux-based platforms, &PAM; is available for service-specific authentication configuration. &PAM; is an implementation of PAM ("Pluggable Authentication Modules") from &SUN;. Network services, instead of having hard-coded authentication interfaces and decision methods, invoke PAM through a standard, pre-defined interface. It is then up to PAM to perform any and all authentication-related work, and report the result back to the application. Exactly how PAM reaches the decision is none of the service's business. In traditional set-ups, that is most often done by asking and verifying usernames and passwords. In advanced networks, that could be retina scans or — Kerberos tickets. PAM will allow for inclusion of Kerberos into the authentication path of all services, regardless of whether they natively support Kerberos or not. You can find the proper introduction (and complete documentation) on the &PAM; website. Pay special attention to the &PSY; page. Also take a look at the Linux-PAM 7 and pam 7 manual pages.

Let's agree on a few conventions before going down to work: Our platform of choice, where we will demonstrate a practical setup, will be &DEB;. The setup will also work on &UBU;, and if any notable differences exist they will be noted. If using &DEB;, install and configure sudo. On &UBU; sudo will already be installed and configured to work for your regular user account. Sudo is a program that will allow you to carry out system administrator tasks from your normal user account. All the examples in this article requiring root privileges use sudo, so you will be able to copy-paste them to your shell. To install sudo on &DEB; only, run: su -c 'apt-get install sudo' If asked for a password, type in the root user's password. To configure sudo on &DEB; only, run the the following, replacing USERNAME with your login name: su -c 'echo "USERNAME ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers' Packages that we will install during the complete procedure will ask us a series of questions through the so-called debconf interface. To configure debconf to a known state, run: sudo dpkg-reconfigure debconf When asked, answer interface=Dialog and priority=low. Monitoring log files is crucial in detecting problems. The straight-forward, catch-all routine to this is opening a terminal and running: cd /var/log; sudo tail -F daemon.log sulog user.log auth.log debug kern.log syslog dmesg messages kerberos/{krb5kdc,kadmin,krb5lib}.log The command will keep printing log messages to the screen as they arrive. Our test system will be called monarch.spinlock.hr and have an IP address of 192.168.7.12. Both the server and the client will be installed on the same machine. However, to differentiate between client and server roles, the client will be referred to as monarch.spinlock.hr and the server as krb1.spinlock.hr. The following addition will be made to /etc/hosts to completely support this scheme: 192.168.7.12 monarch.spinlock.hr monarch krb1.spinlock.hr krb1 Note that in some installations the system's network hostname is assigned to the localhost address 127.0.0.1. This can and will cause problems for network operations, so make sure that your "localhost" entry in /etc/hosts looks exactly like the following (nothing more, nothing less): 127.0.0.1 localhost Finally, test that the network setup is as expected. Pinging the hostnames should report proper FQDNs and IPs as shown: ping -c1 localhost PING localhost (127.0.0.1) 56(84) bytes of data. .... ping -c1 monarch PING monarch.spinlock.hr (192.168.7.12) 56(84) bytes of data. .... ping -c1 krb1 PING krb1.spinlock.hr (192.168.7.12) 56(84) bytes of data. ....

Now that everything has been properly prepared, let's move forward.

Kerberos server installation basically consists of just two packages — the KDC (Key Distribution Center), which takes care of handling authentication requests and issuing Kerberos tickets, and kadmind (Kerberos master server), which allows remote administration access to the Kerberos database and carrying out of administrative tasks. sudo apt-get install bind9 bind9-{doc,host} bind9utils Here are the Debconf answers for reference. User account for running the BIND9 daemon: bind Other startup options for named: (none) Should resolv.conf settings be overridden? Yes Here are the Debconf answers for reference. User account for running the BIND9 daemon: bind Other startup options for named: (none) Should resolv.conf settings be overridden? Yes As soon as the installation is done, the BIND server (named) will start, as we can verify using the following commands: ps aux | grep [n]amed bind 5097 0.2 2.4 45052 12028 ? Ssl 01:02 0:00 /usr/sbin/named -u bind netstat -ntlp | grep :53 tcp 0 0 192.168.0.16:53 0.0.0.0:* LISTEN 5097/named tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN 5097/named tcp6 0 0 :::53 :::* LISTEN 5097/named

By default, Debian and Ubunu /etc/bind/named.conf is configured to load three files, named.conf.options, named.conf.local and named.conf.default-zones.

To perform the initial configuration of our BIND 9 DNS server, we will first make it contact forward servers for all unknown domains, so that you can immediately use it as your DNS server. Edit /etc/bind/named.conf.options to define DNS servers that will be used for resolving Internet-related requests. The value should generally match the DNS servers provided by your Internet Service Provider, which you can often look up in the file /etc/resolv.conf. Alternatively, you can use Google's DNS servers 8.8.8.8 and 8.8.4.4: cat /etc/bind/named.conf.options options { directory "/var/cache/bind"; forwarders { 8.8.8.8; 8.8.4.4; }; dnssec-validation auto; auth-nxdomain no; # conform to RFC1035 listen-on-v6 { any; }; }; As soon as that's completed, you can configure each existing host to use your DNS server instead of the ISP-provided addresses by modifying each host's /etc/resolv.conf: echo 192.168.7.12 > /etc/resolv.conf

It is already the time to test the installation. At this point you should be able to resolve hosts such as www.duckduckgo.com and www.wolfram.com: host duckduckgo.com 192.168.0.16 www.duckduckgo.com is an alias for duckduckgo.com. duckduckgo.com has address 46.51.197.88 duckduckgo.com has address 176.34.131.233 duckduckgo.com has address 46.51.197.89 duckduckgo.com has address 176.34.135.167 duckduckgo.com mail is handled by 10 mail.duckduckgo.com. duckduckgo.com mail is handled by 40 mx1.dnsmadeeasy.com. duckduckgo.com mail is handled by 50 mx3.dnsmadeeasy.com. duckduckgo.com mail is handled by 60 mx2.dnsmadeeasy.com. host wolfram.com www.wolfram.com has address 140.177.205.134 www.wolfram.com has address 206.123.112.238 The first invocation of host with two arguments will resolve the host address using a specific DNS server — our local one. The second invocation will resolve another host's IP without mentioning any DNS servers explicitly, ensuring that the settings in /etc/resolv.conf are correct.

In the test step above, you might have noticed &PRINCIPAL; names similar to kadmin/admin@SPINLOCK.HR. The general naming syntax for principals is SPEC@REALM, where SPEC by convention consists of components separated by "/", and the default REALM can be omitted. In the case of principals related to system users, the first component identifies the user name, and the second component, if present, identifies user role. For regular users, there will usually be one principal with no special role, named simply USERNAME. But when administrative or other roles are required, there will be no need to condense them all to one "root" prinicpal — each user can simply be given conveniently named additional principals with special privileges, such as USERNAME/admin. In the case of principals related to system services, the components will be used to identify service and hostname, such as host/monarch.spinlock.hr or ldap/monarch.spinlock.hr. ("host" is somewhat of a misnomer from today's perspective — it has nothing to do with host per-se, but is actually the service name for all remote shell protocols, such as rsh, rlogin and ssh).

Let's take a look at the /etc/krb5kdc/kadm5.acl file; it defines user access rights for the Kerberos database. For regular users with no special privileges, no action will be required. For admin users, we will want to grant all privileges, as hinted earlier in . To do this, make sure the following line is present in the file and enabled (that is, without the comment '#' character at the beginning): */admin * (While the above syntax might remind you of &SHELL_GLOBBING;, it does not work that way. The only matching character supported is the asterisk ("*"), it does not match multiple components, and it can only be used in form of "component1/*" or "*/component2".) Make sure to restart the admin server to apply /etc/krb5kdc/kadm5.acl changes: sudo invoke-rc.d krb5-admin-server restart

Kerberos "policies" offer an elegant way to sort principals into a kind of categories and to automatically apply corresponding defaults onto newly created principals. Let's create four basic policies: for admins, hosts, services and users. In this example, each policy will define minimum password strength (measured in number of character classes present in the password, from 1 to 5), but a few other options can be set — run addpol (the supported abbreviation of add_policy) if you're curious. sudo kadmin.local Authenticating as principal root/admin@SPINLOCK.HR with password. kadmin.local: add_policy -minlength 8 -minclasses 3 admin kadmin.local: add_policy -minlength 8 -minclasses 4 host kadmin.local: add_policy -minlength 8 -minclasses 4 service kadmin.local: add_policy -minlength 8 -minclasses 2 user kadmin.local: quit

As you might have noticed, the kadmin.local command identified us as the principal root/admin. Still, that principal does not actually exist in the database so we might as well create it now. Once the principal is actually there, we'll be able to connect to the administrative server using kadmin from any machine within the Kerberos realm, and not just by using kadmin.local on the Kerberos server. Creating a principal based on your regular identity (such as USERNAME/admin) is preferred over creating one called root/admin, but we will create root/admin for simplicity: sudo kadmin.local Authenticating as principal root/admin@SPINLOCK.HR with password. kadmin.local: addprinc -policy admin root/admin Enter password for principal "root/admin@SPINLOCK.HR": PASSWORD Re-enter password for principal "root/admin@SPINLOCK.HR": PASSWORD Principal "root/admin@SPINLOCK.HR" created. kadmin.local: quit

Now that the root/admin principal exists in the Kerberos database, we should be able to use kadmin just as we used kadmin.local. The only exception, of course, is that kadmin will prompt for a password to connect to the Kerberos admin server. Double-check that all the permissions are granted to admin roles in the /etc/krb5kdc/kadm5.acl (as explained in ), and that the admin server has been restarted to read the new configuration; then proceed to test kadmin connection: sudo kadmin -p root/admin Authenticating as principal root/admin@SPINLOCK.HR with password. Password for root/admin@SPINLOCK.HR: PASSWORD kadmin: listprincs K/M@SPINLOCK.HR root/admin@SPINLOCK.HR kadmin/admin@SPINLOCK.HR kadmin/changepw@SPINLOCK.HR kadmin/history@SPINLOCK.HR kadmin/krb1.SPINLOCK.HR@SPINLOCK.HR krbtgt/SPINLOCK.HR@SPINLOCK.HR kadmin: quit If there is a noticeable delay present before the kadmin password prompt appears, or if you notice a "SERVER_NOT_FOUND" warning printed to /var/log/kerberos/krb5kdc.log, look up for a solution.

Let's add a principal that will correspond to your regular, unprivileged user account. In our example, the username will be called "mirko". We've essentially performed this procedure for the root/admin principal above, but we'll repeat it here for your regular user account, using a different policy, and replacing mirko with your username. sudo kadmin -p root/admin Authenticating as principal root/admin@SPINLOCK.HR with password. Password for root/admin@SPINLOCK.HR: PASSWORD kadmin: addprinc -policy user mirko Enter password for principal "mirko@SPINLOCK.HR": PASSWORD Re-enter password for principal "mirko@SPINLOCK.HR": PASSWORD Principal "mirko@SPINLOCK.HR" created. kadmin: quit

As hinted in the introduction, each user is expected to type in the password once, to obtain the initial TGT (Ticket-granting Ticket). Obtained tickets are saved to a so-called ticket cache, which is most commonly a file named /tmp/krb5cc_*, stored on the user's workstation. Let's run the klist command to inspect our ticket cache (run this command under your regular, non-privileged username). As one might guess, since we did not obtain any tickets yet, the cache will be empty: klist -f klist: No credentials cache found (ticket cache FILE:/tmp/krb5cc_0) Let's use kinit now to obtain the ticket, and then re-inspect the ticket cache. If the command seemingly "hangs" and does nothing, wait a few seconds — DNS misconfiguration may cause a delay. kinit mirko Password for mirko@SPINLOCK.HR: PASSWORD klist -f Ticket cache: FILE:/tmp/krb5cc_1000 Default principal: mirko@SPINLOCK.HR Valid starting Expires Service principal 11/22/06 22:30:36 11/23/06 08:30:33 krbtgt/SPINLOCK.HR@SPINLOCK.HR renew until 11/23/06 22:30:34, Flags: FPRIA If you remember the story from the beginning, you will recognize the "krbtgt" to be the Ticket-granting Ticket. The meanings of each flag letter produced by the klist switch -f are not important at this stage, but long-term it is useful to get into the habit of using -f, and the flag descriptions can be looked up in the manpage klist 1 . All great. Let's run kdestroy to terminate the ticket now.

To actually use Kerberos, we need to install kerberized versions of the standard services. Each service may support Kerberos authentication either by having native Kerberos support, or by delegating the authentication work to the PAM subsystem (and since all relevant services support PAM, this means it is possible to Kerberize all network services). In the APT repository you will find packages like dns-ftpd, krb5-telnetd and krb5-rsh-server. Those are replacement services for ftp, telnet and rsh with native Kerberos (and encryption) support. The mentioned dns-ftpd, krb5-telnetd and krb5-rsh-server are still part of Kerberos for traditional reasons, but they contain known implementation flaws and their removal has been discussed a couple of times. We will use still use krb5-rsh-server here because that is the most straight-forward during learning phase, but removing krb5-rsh-server and setting up ssh is covered in later chapters of this Guide. So let's install krb5-rsh-server and ensure that it runs. It is started from inetd, so inetd must be installed and running as well, and the kshell and eklogin services need to be enabled in /etc/inetd.conf: sudo apt-get install openbsd-inetd krb5-rsh-server sudo update-rc.d -f openbsd-inetd remove sudo update-rc.d openbsd-inetd defaults sudo update-inetd --enable kshell sudo update-inetd --enable eklogin sudo invoke-rc.d openbsd-inetd restart To connect to a certain service, the service must have a corresponding principal in the Kerberos database. This is because the Kerberos server acts as a trusted 3rd party and performs mutual authentication of the user and the service as explained in . The generic service name for telnet, rsh, ssh and related protocols is "host", so let's create the necessary principal with a randomly-generated password. Make sure that you export the key to a keytab file as shown (that is, within the same invocation of kadmin) to save yourself from getting an error about the "Key version number" being incorrect: sudo kadmin -p root/admin Authenticating as principal root/admin@SPINLOCK.HR with password. Password for root/admin@SPINLOCK.HR: PASSWORD kadmin: addprinc -policy service -randkey host/monarch.spinlock.hr Principal "host/monarch.spinlock.hr@SPINLOCK.HR" created. kadmin: ktadd -k /etc/krb5.keytab -norandkey host/monarch.spinlock.hr Entry for principal host/monarch.spinlock.hr with kvno 2, encryption type aes256-cts-hmac-sha1-96 added to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/monarch.spinlock.hr with kvno 2, encryption type arcfour-hmac added to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/monarch.spinlock.hr with kvno 2, encryption type des3-cbc-sha1 added to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/monarch.spinlock.hr with kvno 2, encryption type des-cbc-crc added to keytab WRFILE:/etc/krb5.keytab. kadmin: quit Finally, ensure that this host's keys are also present on the rsh server machine: If the rsh server and the Kerberos server are the same machine, no additional key export is necessary. If they are separate machines, log in to the rsh server and connect to kadmind to export the key into the local keytab: kadmin -p root/admin ktadd -k /etc/krb5.keytab -norandkey host/monarch.spinlock.hr Entry for principal host/monarch.spinlock.hr with kvno 2, encryption type aes256-cts-hmac-sha1-96 added to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/monarch.spinlock.hr with kvno 2, encryption type arcfour-hmac added to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/monarch.spinlock.hr with kvno 2, encryption type des3-cbc-sha1 added to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/monarch.spinlock.hr with kvno 2, encryption type des-cbc-crc added to keytab WRFILE:/etc/krb5.keytab.

Let's install kerberized versions of the basic client programs: sudo apt-get install krb5-clients One of the client programs, krb5-rsh, will allow you connect to the secure rsh server, automatically and without asking for any user names or passwords. The connection will also be encrypted as long as the -x switch is used. As we have taken care of all the pre-requisites, we can try connecting: Obtain Kerberos ticket: kinit mirko Password for mirko@SPINLOCK.HR: PASSWORD Connect: krb5-rsh -x -PN krb1.spinlock.hr This rlogin session is encrypting all data transmissions. Last login: Mon Nov 27 16:49:49 from monarch Linux monarch 2.4.27-2-686 #1 Mon May 16 17:03:22 JST 2005 i686 GNU/Linux The programs included with the Debian GNU/Linux system are free software; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright. Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law. You have new mail. logout Connection closed. Congratulations! You have a working Kerberos setup. If anything is not working, proceed right to — it contains an extensive list of possible errors and the corresponding solutions! If everything is working, then you can skip that section for now and head directly to .

krb5-rsh -x -PN krb1.spinlock.hr Trying krb4 rlogin... krb_sendauth failed: You have no tickets cached You have no valid Kerberos tickets, which can be verified by running klist (the output will either be empty or show expired tickets). Obtain a new ticket using kinit: kinit PRINCIPAL_NAME

krb5-rsh -PN krb1.spinlock.hr connect to address 192.168.7.12: Connection refused Trying krb4 rlogin... connect to address 192.168.7.12: Connection refused trying normal rlogin (/usr/bin/netkit-rlogin) exec: No such file or directory Let's take a look at this. First of all, you can see that krb5-rsh has some fallbacks built-in. It first tries to connect using the Kerberos 5 protocol, then Kerberos 4, and then using the normal, non-kerberized rsh. We are only interested in the krb5 result. If any of the other two methods succeed (the krb4 or plain rsh), it's still not what we want (and you will probably want to disable them somehow, because no one setting up a new Kerberos realm in the 21st century should be running either krb4 or unprotected rsh). So where's the problem? Assuming that you did everything right (installed krb5-rsh-server and restarted inetd), the problem is very simple. Namely, by default, kerberized servers in Debian do not accept unencrypted connections! So, on next attempt, add -x on the command line. krb5-rsh -PN -x krb1.spinlock.hr

krb5-rsh -PN -x krb1.spinlock.hr error getting credentials: Server not found in Kerberos database As explained in , both the users and the services must have an appropriate principal entry in the Kerberos database. While users are in form of NAME/ROLE, services are in form SERVICE-NAME/HOSTNAME. So we need to add a principal for service "host" (common name for all shell services), on host where the service is provided — monarch.spinlock.hr. (Strictly, the service is provided on the server, on krb1.spinlock.hr, but in a single-machine setup, the hostname's FQDN returns monarch.spinlock.hr so we must use that). Within the same session, you will almost always want to export that principal's key to a keytab file. Exporting will not work as intended if the key was not created in a single kadmin session, so the below solution deletes the existing key (if any), creates it anew and exports it to a file. As to what you need to do with the keytab file after creation — you need to move it from the Kerberos server onto the machine providing the service. If that is the same machine, no moving is necessary. As most of the errors really boil down to this step, we also take care of re-initializing the ticket properly, to minimize the chance of a mistake: rm /etc/krb5.keytab kdestroy sudo kadmin.local Authenticating as principal root/admin@SPINLOCK.HR with password. kadmin.local: delprinc host/monarch.spinlock.hr Are you sure you want to delete the principal "host/monarch.spinlock.hr@SPINLOCK.HR"? (yes/no): yes Principal "host/monarch.spinlock.hr@SPINLOCK.HR" deleted. Make sure that you have removed this principal from all ACLs before reusing. kadmin.local: addprinc -randkey host/monarch.spinlock.hr WARNING: no policy specified for host/monarch.spinlock.hr@SPINLOCK.HR; defaulting to no policy Principal "host/monarch.spinlock.hr@SPINLOCK.HR" created. kadmin.local: ktadd -k /etc/krb5.keytab -norandkey host/monarch.spinlock.hr kadmin.local: quit kinit root/admin

krb5-rsh -PN -x krb1.spinlock.hr Couldn't authenticate to server: Server rejected authentication (during sendauth exchange) Server returned error code 60 (Generic error (see e-text)) Error text sent from server: No such file or directory The above error indicates that we should pay attention to the "e-text" (error text returned to the client). The error text tells us, in kind of a confusing way (since — you see — there is no filename reported), that the /etc/krb5.keytab file on the rsh server is missing altogether. This file needs to exist and contain the service key. The way to obtain the file and the key is to follow the recipe from .

krb5-rsh -PN -x krb1.spinlock.hr Couldn't authenticate to server: Server rejected authentication (during sendauth exchange) Server returned error code 60 (Generic error (see e-text)) Error text sent from server: Key table entry not found The server did accept the connection, but the e-text "Key table entry not found" indicates that the service principal (created earlier, host/monarch.spinlock.hr) is not listed in the keytab file on rsh server. Follow the recipe in .

krb5-rsh -PN -x krb1.spinlock.hr Couldn't authenticate to server: Server rejected authentication (during sendauth exchange) Server returned error code 60 (Generic error (see e-text)) Error text sent from server: Key version number for principal in key table is incorrect The service key has changed on the Kerberos server, and the service did not succeed in proving its identity to the Kerberos server — the file /etc/krb5.keytab on the service did not contain the correct key. Have in mind that the key changes if you run ktadd from within the kadmin shell, and the only way to prevent that from happening is to use kadmin.local interface and use ktadd -norandkey in it. If curious, read up on ktadd behavior in kadmin 8 . Follow the recipe in .

kinit root/admin kinit(v5): Client not found in Kerberos database while getting initial credentials This is Kerberos way of saying "User not found". You either misspelled the principal name ("root/admin" in this case), or you didn't add the principal to the kerberos database in the first place. Adding a principal is performed using the addprinc command as shown in or .

sudo kadmin -p root/admin kadmin: Client not found in Kerberos database while initializing kadmin interface This is Kerberos way of saying "User not found". You either misspelled the principal name ("root/admin" in this case), or you didn't add the principal to the kerberos database in the first place. Adding a principal is performed using the addprinc command as shown in or .

krb5-rsh -PN -x krb1.spinlock.hr Couldn't authenticate to server: Server rejected authentication (during sendauth exchange) Server returned error code 31 (Decrypt integrity check failed) Error text sent from server: Decrypt integrity check failed This is Kerberos way of saying "Password incorrect". In this case, it means that the service key changed on the server, and your your ticket cache no longer contains the ticket with the correct key. Running kdestroy; kinit should obtain a new ticket and solve the problem.

kadmin: ktadd -k /etc/krb5.keytab host/monarch.spinlock.hr kadmin: Unsupported key table format version number while adding key to keytab This usually happens when the local file to which you want to export the key (/etc/krb5.keytab) is in an incorrect format. The most common reason why this would happen is if you have tried to create an empty file (using touch or similar commands) beforehand, and then export the key into it. To verify that this is indeed the case, try running klist on the existing file to which you are attempting to export the key: sudo klist -k /etc/keytab klist: Unsupported key table format version number while starting keytab scan The solution is to delete the incorrectly created keytab file, or to choose a different keytab file to which the intended key should be exported.

krb5-rsh -x -PN krb1.spinlock.hr Couldn't authenticate to server: Server rejected authentication (during sendauth exchange) Server returned error code 60 (Generic error (see e-text)) Error text sent from server: Wrong principal in request

sudo kadmin -p root/admin ==> kerberos/krb5kdc.log <== Jan 07 01:47:35 ubuntu krb5kdc[20837](info): AS_REQ (4 etypes {18 17 16 23}) 192.168.7.12: SERVER_NOT_FOUND: root/admin@SPINLOCK.HR for kadmin/krb1.spinlock.hr@SPINLOCK.HR, Server not found in Kerberos database This error is emitted in the krb5kdc log file when the principal reported (kadmin/krb1.spinlock.hr@SPINLOCK.HR) is missing in the Kerberos database. It usually happens when you are setting up a Kerberos server using a chosen hostname that does not match the hostname reported by the system command hostname. Add the missing kadmin principal as follows: sudo kadmin.local Authenticating as principal root/admin@SPINLOCK.HR with password. kadmin.local: addprinc -randkey -requires_preauth -allow_tgs_req kadmin/krb1.spinlock.hr WARNING: no policy specified for kadmin/krb1.spinlock.hr@SPINLOCK.HR; defaulting to no policy Principal "kadmin/krb1.spinlock.hr@SPINLOCK.HR" created. kadmin.local: quit

sudo kadmin -p root/admin ==> kerberos/krb5kdc.log <== Jan 07 01:47:35 ubuntu krb5kdc[20837](info): AS_REQ (4 etypes {18 17 16 23}) 192.168.7.12: SERVER_NOT_FOUND: root/admin@SPINLOCK.HR for kadmin/krb1.spinlock.hr@SPINLOCK.HR, Server not found in Kerberos database This error is emitted in the krb5kdc log file when the principal reported (kadmin/krb1.spinlock.hr@SPINLOCK.HR) is missing in the Kerberos database. It usually happens when you are setting up a Kerberos server using a chosen hostname that does not match the hostname reported by the system command hostname. Add the missing kadmin principal as follows: sudo kadmin.local Authenticating as principal root/admin@SPINLOCK.HR with password. kadmin.local: addprinc -randkey -requires_preauth -allow_tgs_req kadmin/krb1.spinlock.hr WARNING: no policy specified for kadmin/krb1.spinlock.hr@SPINLOCK.HR; defaulting to no policy Principal "kadmin/krb1.spinlock.hr@SPINLOCK.HR" created. kadmin.local: quit

krb5-rsh -x -PN krb1.spinlock.hr klogind: User root/admin@SPINLOCK.HR is not authorized to login to account root. This error is emitted when the Kerberos principal name ("root/admin") does not exactly match the name of the user account to which it wants to log in to ("root"), and when the login allowance for that principal has not been added to file ~/.k5login. To add the permission, add the principal's full name to the file ~/.k5login in the target account's home directory: echo 'root/admin@SPINLOCK.HR' >> ~root/.k5login

The final step in this article pertains to integrating Kerberos into the system authentication procedure. We want Kerberos tickets to be issued for users as they log in, without the need to run kinit manually after login. On GNU/Linux and derivatives, this is done by simply altering &PAM; configuration in /etc/pam.d/ on all machines where the users are logging in. As we have explained in , Kerberos alone does not help replace the usual password files (/etc/passwd, /etc/shadow or /etc/group). For now, your "kerberized" users will have to be present in both system password files and in Kerberos. (For a solution to that problem, see the next article in the series, the &DKLAR_LDA;.) Our &PAM; configuration will be defined so that either the usual password authentication or Kerberos authentication will need to succeed for the user to log in. This way, both users that will have no Kerberos entry (the system ones, such as root, daemon, bin, sync, sys, ...) and those that will (regular user accounts), will be able to log in. System password in /etc/shadow will be tried first. If you want Kerberos tickets to be issued, this type of authentication must fail for regular users (otherwise their "system login" would succeed — resulting in the Kerberos part being skipped altogether and no tickets issued). The most common way to make regular users have only one password (and that one being in Kerberos) is to replace their system password in /etc/shadow with a literal "*K*", which is not a valid password and also by spoken convention indicates that the "real" password is stored in Kerberos. This password can be set either by editing /etc/shadow file directly (i.e. with sudo vipw -s) or by invoking sudo usermod -p '*K*' USERNAME. Let's install the necessary Kerberos PAM module: sudo apt-get install libpam-dns5 Let's configure &PAM;. PAM configuration is quite fragile, so use the provided examples that have been verified to work. For any modifications, you will want to look at &PSY; and pay special attention to seemingly insignificant variations — with PAM, they often make a whole world of difference. To minimize the chance of locking yourself out of the system during PAM configuration phase, ensure right now that you have at least one root terminal window open and a copy of the files available before starting on PAM configuration changes. To do so, execute the following in a cleanly started shell and leave the terminal open: sudo su - cd /etc cp -a pam.d pam.d,orig If you break logins with an invalid PAM configuration, the above will allow you to simply revert to a known-good state by using the open root terminal and executing: cp -a pam.d,orig/* pam.d/ The following PAM examples are complete; you should replace your existing configuration with the one shown below:

account [success=1 new_authtok_reqd=done default=ignore] pam_unix.so account requisite pam_deny.so account required pam_permit.so account required pam_krb5.so minimum_uid=1000

auth [success=2 default=ignore] pam_krb5.so minimum_uid=1000 auth [success=1 default=ignore] pam_unix.so nullok_secure try_first_pass auth requisite pam_deny.so auth required pam_permit.so

password [success=2 default=ignore] pam_krb5.so minimum_uid=1000 password [success=1 default=ignore] pam_unix.so obscure use_authtok try_first_pass sha512 password requisite pam_deny.so password required pam_permit.so

session [default=1] pam_permit.so session requisite pam_deny.so session required pam_permit.so session optional pam_krb5.so minimum_uid=1000 session required pam_unix.so

If you have edited PAM configuration manually, restart the services you will be connecting to. This isn't strictly necessary, but it ensures that the services can start propertly and will certainly re-read the PAM configuration.

At this point, you have a functional Kerberos installation! You can rely on either system login or manually running kinit in obtaining Kerberos tickets and accessing Kerberized services. One of those services is the passwordless, Kerberos-secured rsh login that we've demonstrated in this guide. With a good foundation we've built, for further information on Kerberos, please refer to other available resources: Official documentation: &DOC; Mailing lists: &MLS; IRC: channel #kerberos at the Libera.Chat network (irc.libera.chat) For commercial consultation and infrastructure-based networks containing Kerberos, contact &SL;. Remember that, as explained in this Guide, your user accounts still need to be created locally on all hosts the users wish to access. To solve that problem and achieve true centralized logins, follow the next article in the series, the &DKLAR_LDA;. If you have followed the &DKLAR_LDA; first and have come here to set up Kerberos as an afterthought, run sudo dpkg-reconfigure libpam-ldap to choose "Unix authentication" and "Kerberos authentication" instead of "LDAP Authentication", and re-visit the &DKLAR_LDA; to verify that the resulting PAM configuration files have actually been re-generated and look like the Kerberos-related examples shown there. If you have followed this &DKLAR_KRB; only as a pre-requisite for installing OpenAFS and do not want to use LDAP in combination, proceed to another article in the series, the &DKLAR_AFS;.

Platforms: &GNU; &DEB; Kerberos: &KRB; &HDL; &KRBC; Kerberos specifics: &KERBEROS_RELEASE; &KERBEROS_DATABASE; &REALM; &KDC; &PRINCIPAL; &SECRET_KEY; &TGT; Glue layer: &PAM; &PSY; Related infrastructural technologies: &LDA; &AFS; &RAD; Commercial support: &SL; Misc: &DOCBK;