479 lines
16 KiB
Plaintext
479 lines
16 KiB
Plaintext
1 - Purpose of this document
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============================
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This document describes how to build, install and configure a
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Postfix system so that it can do one of the following:
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- Send mail only, without changing an existing sendmail
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installation.
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- Send and receive mail via a virtual host interface, still
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without any change to an existing sendmail installation.
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- Replace sendmail altogether.
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2 - Typographical conventions
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=============================
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In the instructions below, a command written as
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# command
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should be executed as the superuser.
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A command written as
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% command
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should be executed as an unprivileged user.
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3 - Documentation
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=================
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Documentation is available as HTML web pages (point your browser
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to html/index.html) and as UNIX-style manpages (point your MANPATH
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environment variable to the `man' subdirectory; be sure to use an
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absolute path).
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The sample configuration files in the `conf' directory have extensive
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comments, but they may not describe every nuance of every feature.
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Many files have their own built-in manual page. Tools to extract
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those embedded manual pages are available in the mantools directory.
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4 - Building on a supported system
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==================================
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If your system is supported, it is one of
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AIX 3.2.5
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AIX 4.1.x
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AIX 4.2.0
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BSD/OS 2.x
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BSD/OS 3.x
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BSD/OS 4.x
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FreeBSD 2.x
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FreeBSD 3.x
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FreeBSD 4.x
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HP-UX 9.x
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HP-UX 10.x
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HP-UX 11.x
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IRIX 5.x
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IRIX 6.x
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Linux Debian 1.3.1
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Linux Debian 2.x
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Linux RedHat 4.x
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Linux RedHat 5.x
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Linux RedHat 6.x
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Linux Slackware 3.5
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Linux Slackware 4.0
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Linux Slackware 7.0
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Linux SuSE 5.x
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Linux SuSE 6.x
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Mac OS X server
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NEXTSTEP 3.x
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NetBSD 1.x
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OPENSTEP 4.x
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OSF1.V3 (Digital UNIX)
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OSF1.V4 aka Digital UNIX V4
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OSF1.V5 aka Digital UNIX V5
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OpenBSD 2.x
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Reliant UNIX 5.x
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Rhapsody 5.x
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SunOS 4.1.x
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SunOS 5.4..5.7 (Solaris 2.4..7)
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Ultrix 4.x
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or something closely resemblant.
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If at any time in the build process you get messages like: "make:
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don't know how to ..." you should be able to recover by running
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the following command from the Postfix top-level directory:
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% make -f Makefile.init makefiles
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If you copied the Postfix source code after building it on another
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machine, it is a good idea to cd into the top-level directory and
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% make tidy
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first. This will get rid of any system dependencies left over from
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compiling the software elsewhere.
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To build with GCC, or with the native compiler if people told me
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that is better for your system, just cd into the top-level Postfix
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directory of the source tree and type:
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% make
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To build with a non-default compiler, you need to specify the name
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of the compiler:
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% make makefiles CC=/opt/SUNWspro/bin/cc (Solaris)
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% make
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% make makefiles CC="/opt/ansic/bin/cc -Ae" (HP-UX)
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% make
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% make makefiles CC="purify cc"
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% make
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and so on. In some cases, optimization is turned off automatically.
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In order to build with non-default settings, for example, with a
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configuration directory other than /etc/postfix, use:
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% make makefiles CCARGS=-DDEF_CONFIG_DIR=\\\\\\\"/some/where\\\\\\\"
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% make
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That's seven backslashes :-) But at least this works with sh and csh.
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In any case, if the command
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% make
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produces compiler error messages, it may be time to examine the
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FAQ document.
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5 - Porting to on an unsupported system
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=======================================
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- Choose a SYSTEMTYPE name for the new system. Please use a name
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that includes the major version of the operating system (such as
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SUNOS4 or LINUX2), so that different releases of the same system
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can be supported without confusion.
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- Add a case statement to the "makedefs" shell script in the
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top-level directory that recognizes the new system reliably, and
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that emits the right system-specific information. Be sure to make
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the code robust against user PATH settings; if the system offers
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multiple UNIX flavors (e.g. BSD and SYSV) be sure to build for the
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native flavor, not the emulated one.
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- Add an #ifdef SYSTEMTYPE section to the central util/sys_defs.h
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include file. You may have to invent new feature macros. Please
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choose sensible feature macro names such as HAS_DBM or
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FIONREAD_IN_SYS_FILIO_H. I strongly recommend against #ifdef
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SYSTEMTYPE dependencies in individual source files. This may seem
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to be the quickest solution, but it will create a mess that becomes
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increasingly difficult to maintain over time. Moreover, with the
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next port you'd have to place #ifdefs all over the source code
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again.
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6 - Installing the software after successful compilation
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========================================================
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IMPORTANT: if you are REPLACING an existing sendmail installation
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with Postfix, you may need to keep the old sendmail program running
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for some time in order to flush the mail queue. As superuser,
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execute the following commands (your sendmail, newaliases and mailq
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programs may be in a different place):
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# mv /usr/sbin/sendmail /usr/sbin/sendmail.OFF
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# mv /usr/bin/newaliases /usr/bin/newaliases.OFF
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# mv /usr/bin/mailq /usr/bin/mailq.OFF
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# chmod 755 /usr/sbin/sendmail.OFF /usr/bin/newaliases.OFF \
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/usr/bin/mailq.OFF
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In order to install or upgrade Postfix:
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- Create a user "postfix" with a unique user id and group id.
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Preferably, this is an account that no-one can log into. The
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account does not need an executable login shell, and needs no
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existing home directory. My password file entry looks like this:
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postfix:*:12345:12345:postfix:/no/where:/no/shell
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- Make sure there is a corresponding alias in /etc/aliases:
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postfix: root
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- Review section 12 of this file, and decide if a world-writable
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maildrop is OK, or if Postfix needs a set-gid posting agent.
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- Run the INSTALL.sh script as the super-user:
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# sh INSTALL.sh
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The INSTALL.sh script offers suggestions for pathnames that you
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can override, either by editing INSTALL.sh or by specifying your
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preferences interactively. INSTALL.sh stores your preferences in
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the Postfix configuration directory in order to ease future installs.
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- Proceed to the section on how you wish to run Postfix on your
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particular machine:
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- Send mail only, without changing an existing sendmail
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installation (section 7).
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- Send and receive mail via a virtual host interface, still
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without any change to an existing sendmail installation
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(section 8).
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- Replace sendmail altogether (section 9).
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7 - Configuring Postfix to send mail only
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=========================================
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If you are going to use Postfix to send mail only, there is no need
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to change your existing sendmail setup. Instead, set up your mail
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user agent so that it calls the Postfix sendmail program directly.
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Follow the instructions in the "Mandatory configuration file edits"
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in section 10, review the "To chroot or not to chroot" text in
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section 11, and choose a security model according to section 12.
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You MUST comment out the `smtp inet' entry in /etc/postfix/master.cf,
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in order to avoid conflicts with the real sendmail.
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Start the Postfix system:
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# postfix start
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or, if you feel nostalgic, use the Postfix sendmail command:
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# sendmail -bd -qwhatever
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and watch your syslog file for any error messages.
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When it is run for the first time, the Postfix startup shell script
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will create a bunch of subdirectories below the Postfix spool
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directory.
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In order to inspect the mail queue, use
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% sendmail -bp
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See also the "Care and feeding" section 13 below.
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8 - Configuring Postfix to send and receive mail (virtual interface)
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====================================================================
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Alternatively, you can use the Postfix system to send AND receive
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mail while leaving your sendmail setup intact, by running Postfix
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on a virtual interface address. Simply configure your mail user
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agent to directly invoke the Postfix sendmail program.
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The examples/virtual-setup directory gives instructions for setting
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up virtual interfaces for a variety of UNIX versions.
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In the /etc/postfix/main.cf file, I would specify
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myhostname = virtual.host.name
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inet_interfaces = $myhostname
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mydestination = $myhostname
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Follow the instructions in the "Mandatory configuration file edits"
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in section 10, review the "To chroot or not to chroot" text in
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section 11, and choose a security model according to section 12.
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Start the mail system:
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# postfix start
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or, if you feel nostalgic, use the Postfix sendmail program:
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# sendmail -bd -qwhatever
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and watch your syslog file for any error messages.
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When it is run for the first time, the Postfix startup shell script
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will create a bunch of subdirectories below the Postfix spool
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directory.
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In order to inspect the mail queue, use
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% sendmail -bp
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See also the "Care and feeding" section 13 below.
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9 - Turning off sendmail forever
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================================
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Prior to installing Postfix you should save the existing sendmail
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program files as described in section 6.
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Be sure to keep the old sendmail running for at least a couple
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days to flush any unsent mail. To do so, stop the sendmail daemon
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and restart it as:
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# /usr/sbin/sendmail.OFF -q
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After you have visited the "Mandatory configuration file edits"
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section below, you can start the Postfix system with
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# postfix start
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But the good old sendmail way works just as well:
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# sendmail -bd -qwhatever
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and watch the syslog file for any complaints from the mail system.
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When it is run for the first time, the Postfix startup shell script
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will create a bunch of subdirectories below the Postfix spool
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directory.
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See also the "Care and feeding" section 13 below.
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10 - Mandatory configuration file edits
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=======================================
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By default, Postfix configuration files are in /etc/postfix, and
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must be owned by root. Giving someone else write permission to
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main.cf or master.cf means giving root privileges to that person.
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Whenever you make a change to a config file, execute the following
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command in order to refresh a running mail system:
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# postfix reload
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In /etc/postfix/main.cf you will have to set up a minimal number of
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configuration parameters. Postfix configuration parameters
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resemble shell variables. You specify a variable as
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parameter = value
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and you use it by putting a $ in front of its name:
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other_parameter = $parameter
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You can use $parameter before it is given a value. The Postfix
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configuration language uses lazy evaluation, and does not look at
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a parameter value until it is needed at runtime.
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First of all, you must specify what domain will be appended to a
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local address. The "myorigin" parameter defaults to the local
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hostname, but that is probably OK only for very small sites.
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Some examples:
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myorigin = $myhostname
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myorigin = $mydomain
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In the first case, local mail goes out as user@$myhostname, in
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the second case the sender address is user@$mydomain.
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Next you need to specify what mail addresses are local to the
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Postfix system.
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Some examples:
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mydestination = $myhostname, localhost.$mydomain
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mydestination = $myhostname, localhost.$mydomain, $mydomain
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mydestination = $myhostname
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The first example is appropriate for a workstation, the second is
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appropriate for the mailserver for an entire domain. The third
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example should be used when running on a virtual host interface.
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If you're behind a firewall, you should set up a relayhost. If
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you can, specify the organizational domain name so that Postfix
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can use DNS lookups, and so that it can fall back to a secondary
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MX host when the primary MX host is down. Otherwise just specify
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a hard-coded hostname.
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Some examples:
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relayhost = $mydomain
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relayhost = mail.$mydomain
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relayhost = [mail.$mydomain]
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The form enclosed with [] eliminates DNS MX lookups.
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By default, the SMTP client will do DNS lookups for sender and
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recipient addresses even when you specify a relay host. If your
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machine has no access to a DNS server, turn off SMTP client DNS
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lookups like this:
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disable_dns_lookups = yes
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The FAQ (html/faq.html) has more hints and tips for firewalled
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and/or dial-up networks.
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Finally, if you haven't used Sendmail prior to using Postfix, you
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will have to build the alias database (with: sendmail -bi, or:
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newaliases). Be sure to set up aliases for root and postmaster that
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forward mail to a real person.
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11 - To chroot or not to chroot
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==============================
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Most Postfix daemons can run in a chroot jail, that is, in a chroot
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environment at fixed low privilege. This provides a significant
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barrier against intrusion. The barrier is not impenetrable, but
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every little bit helps.
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The file /etc/postfix/master.cf by default runs no Postfix daemons
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in a chroot jail. However, with the exception of the `local' and
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`pipe' daemons, every Postfix daemon can run chrooted.
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The examples/chroot-setup directory has a collection of scripts
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for setting up chroot environments for Postfix systems.
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12 - Security: writable versus protected maildrop directory
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===========================================================
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Postfix offers a choice of submission mechanims.
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1 - Postfix can use a world-writable, sticky, mode 1733 maildrop
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directory where local users can submit mail. This approach
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avoids the need for set-uid or set-gid software. Mail can be
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posted even while the mail system is down. Queue files in the
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maildrop directory have no read/write/execute permission for
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other users. The maildrop directory is not used for mail
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received via the network.
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With directory world write permission come opportunities for
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annoyance: a local user can make hard links to someone else's
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maildrop files so they don't go away and may be delivered
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multiple times; a local user can fill the maildrop directory
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with junk and try to crash the mail system; and a local user
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can hard link someone else's files into the maildrop directory
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and try to have them delivered as mail. However, Postfix queue
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files have a specific format; less than one in 10^12 non-Postfix
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files would be recognized as a valid Postfix queue file.
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In order to enable maildrop world-write permission:
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- Specify "no" when asked by the INSTALL.sh script whether
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Postfix needs set-gid privileges.
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2 - On systems with many users it may be desirable to revoke maildrop
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directory world write permission, and to enable set-gid privileges
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on a small "maildrop" command that is provided for this purpose.
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In order to revoke maildrop world-write permission:
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- Create a group "maildrop" that is unique and that does not
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share its group ID with any other user, certainly not with
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the postfix account,
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- Specify "maildrop" when asked by the INSTALL.sh script whether
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Postfix needs set-gid privileges.
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The sendmail posting program will automatically invoke the
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postdrop command when maildrop directory write permission is
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restricted.
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13 - Care and feeding of the Postfix system
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===========================================
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The Postfix programs log all problems to the syslog daemon. The
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names of logfiles are specified in /etc/syslog.conf. Note: the
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syslogd will not create files. You must create them ahead of time
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before (re)starting syslogd. At the very least you need something
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like:
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mail.err /dev/console
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mail.debug /var/log/maillog
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Hopefully, the number of problems will be small, but it is a good
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idea to run every night before the syslog files are rotated:
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# postfix check
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# egrep '(reject|warning|error|fatal|panic):' /some/log/file
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The second line looks for problem reports from the mail software,
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and reports how effective the anti-relay and anti-UCE blocks are.
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