Exim is distributed as a gzipped or bzipped tar file which, when unpacked, creates a directory with the name of the current release (for example, exim-4.97.1) into which the following files are placed:
|contains some acknowledgments
|contains a reference to where changes are documented
|the GNU General Public Licence
|top-level make file
|conditions for the use of Exim
|list of files, directories and simple build instructions
Other files whose names begin with README may also be present. The following subdirectories are created:
|an empty directory for local configuration files
|source files for the Exim monitor
|scripts used in the build process
|remaining source files
The main utility programs are contained in the src directory and are built with the Exim binary. The util directory contains a few optional scripts that may be useful to some sites.
2. Multiple machine architectures and operating systems
The building process for Exim is arranged to make it easy to build binaries for a number of different architectures and operating systems from the same set of source files. Compilation does not take place in the src directory. Instead, a build directory is created for each architecture and operating system. Symbolic links to the sources are installed in this directory, which is where the actual building takes place. In most cases, Exim can discover the machine architecture and operating system for itself, but the defaults can be overridden if necessary. A C99-capable compiler will be required for the build.
3. PCRE2 library
Exim no longer has an embedded regular-expression library as the vast majority of modern systems include PCRE2 as a system library, although you may need to install the PCRE2 package or the PCRE2 development package for your operating system. If your system has a normal PCRE2 installation the Exim build process will need no further configuration. If the library or the headers are in an unusual location you will need to either set the PCRE2_LIBS and INCLUDE directives appropriately, or set PCRE2_CONFIG=yes to use the installed pcre-config command. If your operating system has no PCRE2 support then you will need to obtain and build the current PCRE2 from https://github.com/PhilipHazel/pcre2/releases. More information on PCRE2 is available at https://www.pcre.org/.
4. DBM libraries
Even if you do not use any DBM files in your configuration, Exim still needs a DBM library in order to operate, because it uses indexed files for its hints databases. Unfortunately, there are a number of DBM libraries in existence, and different operating systems often have different ones installed.
If you are using Solaris, IRIX, one of the modern BSD systems, or a modern Linux distribution, the DBM configuration should happen automatically, and you may be able to ignore this section. Otherwise, you may have to learn more than you would like about DBM libraries from what follows.
Licensed versions of Unix normally contain a library of DBM functions operating via the ndbm interface, and this is what Exim expects by default. Free versions of Unix seem to vary in what they contain as standard. In particular, some early versions of Linux have no default DBM library, and different distributors have chosen to bundle different libraries with their packaged versions. However, the more recent releases seem to have standardized on the Berkeley DB library.
Different DBM libraries have different conventions for naming the files they use. When a program opens a file called dbmfile, there are several possibilities:
A traditional ndbm implementation, such as that supplied as part of Solaris, operates on two files called dbmfile.dir and dbmfile.pag.
The GNU library, gdbm, operates on a single file. If used via its ndbm compatibility interface it makes two different hard links to it with names dbmfile.dir and dbmfile.pag, but if used via its native interface, the filename is used unmodified.
The Berkeley DB package, if called via its ndbm compatibility interface, operates on a single file called dbmfile.db, but otherwise looks to the programmer exactly the same as the traditional ndbm implementation.
If the Berkeley package is used in its native mode, it operates on a single file called dbmfile; the programmer’s interface is somewhat different to the traditional ndbm interface.
To complicate things further, there are several very different versions of the Berkeley DB package. Version 1.85 was stable for a very long time, releases 2.x and 3.x were current for a while, but the latest versions when Exim last revamped support were numbered 5.x. Maintenance of some of the earlier releases has ceased, and Exim no longer supports versions before 3.x. All versions of Berkeley DB could be obtained from http://www.sleepycat.com/, which is now a redirect to their new owner’s page with far newer versions listed. It is probably wise to plan to move your storage configurations away from Berkeley DB format, as today there are smaller and simpler alternatives more suited to Exim’s usage model.
Yet another DBM library, called tdb, is available from https://sourceforge.net/projects/tdb/files/. It has its own interface, and also operates on a single file.
Exim and its utilities can be compiled to use any of these interfaces. In order to use any version of the Berkeley DB package in native mode, you must set USE_DB in an appropriate configuration file (typically Local/Makefile). For example:
Similarly, for gdbm you set USE_GDBM, and for tdb you set USE_TDB. An error is diagnosed if you set more than one of these. You can set USE_NDBM if needed to override an operating system default.
At the lowest level, the build-time configuration sets none of these options, thereby assuming an interface of type (1). However, some operating system configuration files (for example, those for the BSD operating systems and Linux) assume type (4) by setting USE_DB as their default, and the configuration files for Cygwin set USE_GDBM. Anything you set in Local/Makefile, however, overrides these system defaults.
As well as setting USE_DB, USE_GDBM, or USE_TDB, it may also be necessary to set DBMLIB, to cause inclusion of the appropriate library, as in one of these lines:
DBMLIB = -ldb DBMLIB = -ltdb DBMLIB = -lgdbm -lgdbm_compat
The last of those was for a Linux having GDBM provide emulated NDBM facilities. Settings like that will work if the DBM library is installed in the standard place. Sometimes it is not, and the library’s header file may also not be in the default path. You may need to set INCLUDE to specify where the header file is, and to specify the path to the library more fully in DBMLIB, as in this example:
There is further detailed discussion about the various DBM libraries in the file doc/dbm.discuss.txt in the Exim distribution.
5. Pre-building configuration
Before building Exim, a local configuration file that specifies options independent of any operating system has to be created with the name Local/Makefile. A template for this file is supplied as the file src/EDITME, and it contains full descriptions of all the option settings therein. These descriptions are therefore not repeated here. If you are building Exim for the first time, the simplest thing to do is to copy src/EDITME to Local/Makefile, then read it and edit it appropriately.
There are three settings that you must supply, because Exim will not build without them. They are the location of the runtime configuration file (CONFIGURE_FILE), the directory in which Exim binaries will be installed (BIN_DIRECTORY), and the identity of the Exim user (EXIM_USER and maybe EXIM_GROUP as well). The value of CONFIGURE_FILE can in fact be a colon-separated list of filenames; Exim uses the first of them that exists.
There are a few other parameters that can be specified either at build time or at runtime, to enable the same binary to be used on a number of different machines. However, if the locations of Exim’s spool directory and log file directory (if not within the spool directory) are fixed, it is recommended that you specify them in Local/Makefile instead of at runtime, so that errors detected early in Exim’s execution (such as a malformed configuration file) can be logged.
Exim’s interfaces for calling virus and spam scanning software directly from access control lists are not compiled by default. If you want to include these facilities, you need to set
in your Local/Makefile. For details of the facilities themselves, see chapter 45.
If you are going to build the Exim monitor, a similar configuration process is required. The file exim_monitor/EDITME must be edited appropriately for your installation and saved under the name Local/eximon.conf. If you are happy with the default settings described in exim_monitor/EDITME, Local/eximon.conf can be empty, but it must exist.
This is all the configuration that is needed in straightforward cases for known operating systems. However, the building process is set up so that it is easy to override options that are set by default or by operating-system-specific configuration files, for example, to change the C compiler, which defaults to gcc. See section 4.13 below for details of how to do this.
6. Support for iconv()
The contents of header lines in messages may be encoded according to the rules described RFC 2047. This makes it possible to transmit characters that are not in the ASCII character set, and to label them as being in a particular character set. When Exim is inspecting header lines by means of the $h_ mechanism, it decodes them, and translates them into a specified character set (default is set at build time). The translation is possible only if the operating system supports the iconv() function.
However, some of the operating systems that supply iconv() do not support very many conversions. The GNU libiconv library (available from https://www.gnu.org/software/libiconv/) can be installed on such systems to remedy this deficiency, as well as on systems that do not supply iconv() at all. After installing libiconv, you should add
to your Local/Makefile and rebuild Exim.
7. Including TLS/SSL encryption support
Exim is usually built to support encrypted SMTP connections, using the STARTTLS command as per RFC 2487. It can also support clients that expect to start a TLS session immediately on connection to a non-standard port (see the tls_on_connect_ports runtime option and the -tls-on-connect command line option).
If you want to build Exim with TLS support, you must first install either the OpenSSL or GnuTLS library. There is no cryptographic code in Exim itself for implementing SSL.
If you do not want TLS support you should set
If OpenSSL is installed, you should set
USE_OPENSL=yes TLS_LIBS=-lssl -lcrypto
in Local/Makefile. You may also need to specify the locations of the OpenSSL library and include files. For example:
USE_OPENSSL=yes TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto TLS_INCLUDE=-I/usr/local/openssl/include/
If you have pkg-config available, then instead you can just use:
If GnuTLS is installed, you should set
USE_GNUTLS=yes TLS_LIBS=-lgnutls -ltasn1 -lgcrypt
in Local/Makefile, and again you may need to specify the locations of the library and include files. For example:
USE_GNUTLS=yes TLS_LIBS=-L/usr/gnu/lib -lgnutls -ltasn1 -lgcrypt TLS_INCLUDE=-I/usr/gnu/include
If you have pkg-config available, then instead you can just use:
You do not need to set TLS_INCLUDE if the relevant directory is already specified in INCLUDE. Details of how to configure Exim to make use of TLS are given in chapter 43.
8. Use of tcpwrappers
Exim can be linked with the tcpwrappers library in order to check incoming SMTP calls using the tcpwrappers control files. This may be a convenient alternative to Exim’s own checking facilities for installations that are already making use of tcpwrappers for other purposes. To do this, you should set USE_TCP_WRAPPERS in Local/Makefile, arrange for the file tcpd.h to be available at compile time, and also ensure that the library libwrap.a is available at link time, typically by including -lwrap in EXTRALIBS_EXIM. For example, if tcpwrappers is installed in /usr/local, you might have
USE_TCP_WRAPPERS=yes CFLAGS=-O -I/usr/local/include EXTRALIBS_EXIM=-L/usr/local/lib -lwrap
in Local/Makefile. The daemon name to use in the tcpwrappers control files is “exim”. For example, the line
exim : LOCAL 192.168.1. .friendly.domain.example
in your /etc/hosts.allow file allows connections from the local host, from the subnet 192.168.1.0/24, and from all hosts in friendly.domain.example. All other connections are denied. The daemon name used by tcpwrappers can be changed at build time by setting TCP_WRAPPERS_DAEMON_NAME in Local/Makefile, or by setting tcp_wrappers_daemon_name in the configure file. Consult the tcpwrappers documentation for further details.
9. Including support for IPv6
Exim contains code for use on systems that have IPv6 support. Setting
HAVE_IPV6=YES in Local/Makefile causes the IPv6 code to be included;
it may also be necessary to set IPV6_INCLUDE and IPV6_LIBS on systems
where the IPv6 support is not fully integrated into the normal include and
Two different types of DNS record for handling IPv6 addresses have been defined. AAAA records (analogous to A records for IPv4) are in use, and are currently seen as the mainstream. Another record type called A6 was proposed as better than AAAA because it had more flexibility. However, it was felt to be over-complex, and its status was reduced to “experimental”. Exim used to have a compile option for including A6 record support but this has now been withdrawn.
10. Dynamically loaded lookup module support
On some platforms, Exim supports not compiling all lookup types directly into the main binary, instead putting some into external modules which can be loaded on demand. This permits packagers to build Exim with support for lookups with extensive library dependencies without requiring all users to install all of those dependencies. Most, but not all, lookup types can be built this way.
LOOKUP_MODULE_DIR to the directory into which the modules will be
installed; Exim will only load modules from that directory, as a security
measure. You will need to set
CFLAGS_DYNAMIC if not already defined
for your OS; see OS/Makefile-Linux for an example.
Some other requirements for adjusting
EXTRALIBS may also be necessary,
see src/EDITME for details.
Then, for each module to be loaded dynamically, define the relevant
LOOKUP_<lookup_type> flags to have the value "2" instead of "yes".
For example, this will build in lsearch but load sqlite and mysql support
LOOKUP_LSEARCH=yes LOOKUP_SQLITE=2 LOOKUP_MYSQL=2
11. The building process
Once Local/Makefile (and Local/eximon.conf, if required) have been created, run make at the top level. It determines the architecture and operating system types, and creates a build directory if one does not exist. For example, on a Sun system running Solaris 8, the directory build-SunOS5-5.8-sparc is created. Symbolic links to relevant source files are installed in the build directory.
If this is the first time make has been run, it calls a script that builds
a make file inside the build directory, using the configuration files from the
Local directory. The new make file is then passed to another instance of
make. This does the real work, building a number of utility scripts, and
then compiling and linking the binaries for the Exim monitor (if configured), a
number of utility programs, and finally Exim itself. The command
makefile can be used to force a rebuild of the make file in the build
directory, should this ever be necessary.
If you have problems building Exim, check for any comments there may be in the README file concerning your operating system, and also take a look at the FAQ, where some common problems are covered.
12. Output from make
The output produced by the make process for compile lines is often very unreadable, because these lines can be very long. For this reason, the normal output is suppressed by default, and instead output similar to that which appears when compiling the 2.6 Linux kernel is generated: just a short line for each module that is being compiled or linked. However, it is still possible to get the full output, by calling make like this:
FULLECHO='' make -e
The value of FULLECHO defaults to “@”, the flag character that suppresses command reflection in make. When you ask for the full output, it is given in addition to the short output.
13. Overriding build-time options for Exim
The main make file that is created at the beginning of the building process consists of the concatenation of a number of files which set configuration values, followed by a fixed set of make instructions. If a value is set more than once, the last setting overrides any previous ones. This provides a convenient way of overriding defaults. The files that are concatenated are, in order:
OS/Makefile-Default OS/Makefile-<ostype> Local/Makefile Local/Makefile-<ostype> Local/Makefile-<archtype> Local/Makefile-<ostype>-<archtype> OS/Makefile-Base
where <ostype> is the operating system type and <archtype> is the architecture type. Local/Makefile is required to exist, and the building process fails if it is absent. The other three Local files are optional, and are often not needed.
The values used for <ostype> and <archtype> are obtained from scripts called scripts/os-type and scripts/arch-type respectively. If either of the environment variables EXIM_OSTYPE or EXIM_ARCHTYPE is set, their values are used, thereby providing a means of forcing particular settings. Otherwise, the scripts try to get values from the uname command. If this fails, the shell variables OSTYPE and ARCHTYPE are inspected. A number of ad hoc transformations are then applied, to produce the standard names that Exim expects. You can run these scripts directly from the shell in order to find out what values are being used on your system.
OS/Makefile-Default contains comments about the variables that are set therein. Some (but not all) are mentioned below. If there is something that needs changing, review the contents of this file and the contents of the make file for your operating system (OS/Makefile-<ostype>) to see what the default values are.
If you need to change any of the values that are set in OS/Makefile-Default or in OS/Makefile-<ostype>, or to add any new definitions, you do not need to change the original files. Instead, you should make the changes by putting the new values in an appropriate Local file. For example, when building Exim in many releases of the Tru64-Unix (formerly Digital UNIX, formerly DEC-OSF1) operating system, it is necessary to specify that the C compiler is called cc rather than gcc. Also, the compiler must be called with the option -std1, to make it recognize some of the features of Standard C that Exim uses. (Most other compilers recognize Standard C by default.) To do this, you should create a file called Local/Makefile-OSF1 containing the lines
If you are compiling for just one operating system, it may be easier to put these lines directly into Local/Makefile.
Keeping all your local configuration settings separate from the distributed files makes it easy to transfer them to new versions of Exim simply by copying the contents of the Local directory.
Exim contains support for doing LDAP, NIS, NIS+, and other kinds of file lookup, but not all systems have these components installed, so the default is not to include the relevant code in the binary. All the different kinds of file and database lookup that Exim supports are implemented as separate code modules which are included only if the relevant compile-time options are set. In the case of LDAP, NIS, and NIS+, the settings for Local/Makefile are:
LOOKUP_LDAP=yes LOOKUP_NIS=yes LOOKUP_NISPLUS=yes
and similar settings apply to the other lookup types. They are all listed in src/EDITME. In many cases the relevant include files and interface libraries need to be installed before compiling Exim. However, there are some optional lookup types (such as cdb) for which the code is entirely contained within Exim, and no external include files or libraries are required. When a lookup type is not included in the binary, attempts to configure Exim to use it cause runtime configuration errors.
Many systems now use a tool called pkg-config to encapsulate information
about how to compile against a library; Exim has some initial support for
being able to use pkg-config for lookups and authenticators. For any given
makefile variable which starts
AUTH_, you can add a new
variable with the
_PC suffix in the name and assign as the value the
name of the package to be queried. The results of querying via the
pkg-config command will be added to the appropriate Makefile variables
+= directives, so your version of make will need to support that
syntax. For instance:
LOOKUP_SQLITE=yes LOOKUP_SQLITE_PC=sqlite3 AUTH_GSASL=yes AUTH_GSASL_PC=libgsasl AUTH_HEIMDAL_GSSAPI=yes AUTH_HEIMDAL_GSSAPI_PC=heimdal-gssapi
Exim can be linked with an embedded Perl interpreter, allowing Perl subroutines to be called during string expansion. To enable this facility,
must be defined in Local/Makefile. Details of this facility are given in chapter 12.
The location of the X11 libraries is something that varies a lot between operating systems, and there may be different versions of X11 to cope with. Exim itself makes no use of X11, but if you are compiling the Exim monitor, the X11 libraries must be available. The following three variables are set in OS/Makefile-Default:
X11=/usr/X11R6 XINCLUDE=-I$(X11)/include XLFLAGS=-L$(X11)/lib
These are overridden in some of the operating-system configuration files. For example, in OS/Makefile-SunOS5 there is
X11=/usr/openwin XINCLUDE=-I$(X11)/include XLFLAGS=-L$(X11)/lib -R$(X11)/lib
If you need to override the default setting for your operating system, place a definition of all three of these variables into your Local/Makefile-<ostype> file.
If you need to add any extra libraries to the link steps, these can be put in a variable called EXTRALIBS, which appears in all the link commands, but by default is not defined. In contrast, EXTRALIBS_EXIM is used only on the command for linking the main Exim binary, and not for any associated utilities.
There is also DBMLIB, which appears in the link commands for binaries that use DBM functions (see also section 4.4). Finally, there is EXTRALIBS_EXIMON, which appears only in the link step for the Exim monitor binary, and which can be used, for example, to include additional X11 libraries.
The make file copes with rebuilding Exim correctly if any of the configuration files are edited. However, if an optional configuration file is deleted, it is necessary to touch the associated non-optional file (that is, Local/Makefile or Local/eximon.conf) before rebuilding.
14. OS-specific header files
The OS directory contains a number of files with names of the form os.h-<ostype>. These are system-specific C header files that should not normally need to be changed. There is a list of macro settings that are recognized in the file OS/os.configuring, which should be consulted if you are porting Exim to a new operating system.
15. Overriding build-time options for the monitor
A similar process is used for overriding things when building the Exim monitor, where the files that are involved are
OS/eximon.conf-Default OS/eximon.conf-<ostype> Local/eximon.conf Local/eximon.conf-<ostype> Local/eximon.conf-<archtype> Local/eximon.conf-<ostype>-<archtype>
As with Exim itself, the final three files need not exist, and in this case the OS/eximon.conf-<ostype> file is also optional. The default values in OS/eximon.conf-Default can be overridden dynamically by setting environment variables of the same name, preceded by EXIMON_. For example, setting EXIMON_LOG_DEPTH in the environment overrides the value of LOG_DEPTH at runtime.
16. Installing Exim binaries and scripts
make install runs the exim_install script with no
arguments. The script copies binaries and utility scripts into the directory
whose name is specified by the BIN_DIRECTORY setting in Local/Makefile.
The install script copies files only if they are newer than the files they are
going to replace. The Exim binary is required to be owned by root and have the
setuid bit set, for normal configurations. Therefore, you must run
install as root so that it can set up the Exim binary in this way. However, in
some special situations (for example, if a host is doing no local deliveries)
it may be possible to run Exim without making the binary setuid root (see
chapter 56 for details).
Exim’s runtime configuration file is named by the CONFIGURE_FILE setting in Local/Makefile. If this names a single file, and the file does not exist, the default configuration file src/configure.default is copied there by the installation script. If a runtime configuration file already exists, it is left alone. If CONFIGURE_FILE is a colon-separated list, naming several alternative files, no default is installed.
One change is made to the default configuration file when it is installed: the default configuration contains a router that references a system aliases file. The path to this file is set to the value specified by SYSTEM_ALIASES_FILE in Local/Makefile (/etc/aliases by default). If the system aliases file does not exist, the installation script creates it, and outputs a comment to the user.
The created file contains no aliases, but it does contain comments about the aliases a site should normally have. Mail aliases have traditionally been kept in /etc/aliases. However, some operating systems are now using /etc/mail/aliases. You should check if yours is one of these, and change Exim’s configuration if necessary.
The default configuration uses the local host’s name as the only local domain, and is set up to do local deliveries into the shared directory /var/mail, running as the local user. System aliases and .forward files in users’ home directories are supported, but no NIS or NIS+ support is configured. Domains other than the name of the local host are routed using the DNS, with delivery over SMTP.
It is possible to install Exim for special purposes (such as building a binary distribution) in a private part of the file system. You can do this by a command such as
make DESTDIR=/some/directory/ install
This has the effect of pre-pending the specified directory to all the file paths, except the name of the system aliases file that appears in the default configuration. (If a default alias file is created, its name is modified.) For backwards compatibility, ROOT is used if DESTDIR is not set, but this usage is deprecated.
Running make install does not copy the Exim 4 conversion script convert4r4. You will probably run this only once if you are upgrading from Exim 3. None of the documentation files in the doc directory are copied, except for the info files when you have set INFO_DIRECTORY, as described in section 4.17 below.
For the utility programs, old versions are renamed by adding the suffix .O to their names. The Exim binary itself, however, is handled differently. It is installed under a name that includes the version number and the compile number, for example, exim-4.97.1-1. The script then arranges for a symbolic link called exim to point to the binary. If you are updating a previous version of Exim, the script takes care to ensure that the name exim is never absent from the directory (as seen by other processes).
If you want to see what the make install will do before running it for real, you can pass the -n option to the installation script by this command:
make INSTALL_ARG=-n install
The contents of the variable INSTALL_ARG are passed to the installation script. You do not need to be root to run this test. Alternatively, you can run the installation script directly, but this must be from within the build directory. For example, from the top-level Exim directory you could use this command:
(cd build-SunOS5-5.5.1-sparc; ../scripts/exim_install -n)
There are two other options that can be supplied to the installation script.
-no_chown bypasses the call to change the owner of the installed binary to root, and the call to make it a setuid binary.
-no_symlink bypasses the setting up of the symbolic link exim to the installed binary.
INSTALL_ARG can be used to pass these options to the script. For example:
make INSTALL_ARG=-no_symlink install
The installation script can also be given arguments specifying which files are to be copied. For example, to install just the Exim binary, and nothing else, without creating the symbolic link, you could use:
make INSTALL_ARG='-no_symlink exim' install
17. Installing info documentation
Not all systems use the GNU info system for documentation, and for this reason, the Texinfo source of Exim’s documentation is not included in the main distribution. Instead it is available separately from the FTP site (see section 1.5).
If you have defined INFO_DIRECTORY in Local/Makefile and the Texinfo
source of the documentation is found in the source tree, running
install automatically builds the info files and installs them.
18. Setting up the spool directory
When it starts up, Exim tries to create its spool directory if it does not exist. The Exim uid and gid are used for the owner and group of the spool directory. Sub-directories are automatically created in the spool directory as necessary.
Having installed Exim, you can check that the runtime configuration file is syntactically valid by running the following command, which assumes that the Exim binary directory is within your PATH environment variable:
If there are any errors in the configuration file, Exim outputs error messages. Otherwise it outputs the version number and build date, the DBM library that is being used, and information about which drivers and other optional code modules are included in the binary. Some simple routing tests can be done by using the address testing option. For example,
exim -bt <local username>
should verify that it recognizes a local mailbox, and
exim -bt <remote address>
a remote one. Then try getting it to deliver mail, both locally and remotely. This can be done by passing messages directly to Exim, without going through a user agent. For example:
exim -v email@example.com From: firstname.lastname@example.org To: email@example.com Subject: Testing Exim This is a test message. ^D
The -v option causes Exim to output some verification of what it is doing. In this case you should see copies of three log lines, one for the message’s arrival, one for its delivery, and one containing “Completed”.
If you encounter problems, look at Exim’s log files (mainlog and paniclog) to see if there is any relevant information there. Another source of information is running Exim with debugging turned on, by specifying the -d option. If a message is stuck on Exim’s spool, you can force a delivery with debugging turned on by a command of the form
exim -d -M <exim-message-id>
You must be root or an “admin user” in order to do this. The -d option produces rather a lot of output, but you can cut this down to specific areas. For example, if you use -d-all+route only the debugging information relevant to routing is included. (See the -d option in chapter 5 for more details.)
One specific problem that has shown up on some sites is the inability to do local deliveries into a shared mailbox directory, because it does not have the “sticky bit” set on it. By default, Exim tries to create a lock file before writing to a mailbox file, and if it cannot create the lock file, the delivery is deferred. You can get round this either by setting the “sticky bit” on the directory, or by setting a specific group for local deliveries and allowing that group to create files in the directory (see the comments above the local_delivery transport in the default configuration file). Another approach is to configure Exim not to use lock files, but just to rely on fcntl() locking instead. However, you should do this only if all user agents also use fcntl() locking. For further discussion of locking issues, see chapter 26.
One thing that cannot be tested on a system that is already running an MTA is the receipt of incoming SMTP mail on the standard SMTP port. However, the -oX option can be used to run an Exim daemon that listens on some other port, or inetd can be used to do this. The -bh option and the exim_checkaccess utility can be used to check out policy controls on incoming SMTP mail.
Testing a new version on a system that is already running Exim can most easily be done by building a binary with a different CONFIGURE_FILE setting. From within the runtime configuration, all other file and directory names that Exim uses can be altered, in order to keep it entirely clear of the production version.
20. Replacing another MTA with Exim
Building and installing Exim for the first time does not of itself put it in general use. The name by which the system’s MTA is called by mail user agents is either /usr/sbin/sendmail, or /usr/lib/sendmail (depending on the operating system), and it is necessary to make this name point to the exim binary in order to get the user agents to pass messages to Exim. This is normally done by renaming any existing file and making /usr/sbin/sendmail or /usr/lib/sendmail a symbolic link to the exim binary. It is a good idea to remove any setuid privilege and executable status from the old MTA. It is then necessary to stop and restart the mailer daemon, if one is running.
Some operating systems have introduced alternative ways of switching MTAs. For example, if you are running FreeBSD, you need to edit the file /etc/mail/mailer.conf instead of setting up a symbolic link as just described. A typical example of the contents of this file for running Exim is as follows:
sendmail /usr/exim/bin/exim send-mail /usr/exim/bin/exim mailq /usr/exim/bin/exim -bp newaliases /usr/bin/true
Once you have set up the symbolic link, or edited /etc/mail/mailer.conf, your Exim installation is “live”. Check it by sending a message from your favourite user agent.
You should consider what to tell your users about the change of MTA. Exim may have different capabilities to what was previously running, and there are various operational differences such as the text of messages produced by command line options and in bounce messages. If you allow your users to make use of Exim’s filtering capabilities, you should make the document entitled Exim’s interface to mail filtering available to them.
21. Running the daemon
The most common command line for launching the Exim daemon looks like
exim -bd -q5m
This starts a daemon which
listens for incoming smtp connections, launching handler processes for each new one
starts a queue-runner process every five minutes, to inspect queued messages and run delivery attempts on any that have arrived at their retry time
Should a queue run take longer than the time between queue-runner starts, they will run in parallel. Numbers of jobs of the various types are subject to policy controls defined in the configuration.
22. Upgrading Exim
If you are already running Exim on your host, building and installing a new version automatically makes it available to MUAs, or any other programs that call the MTA directly. However, if you are running an Exim daemon, you do need to send it a HUP signal, to make it re-execute itself, and thereby pick up the new binary. You do not need to stop processing mail in order to install a new version of Exim. The install script does not modify an existing runtime configuration file.
23. Stopping the Exim daemon on Solaris
The standard command for stopping the mailer daemon on Solaris is
If /usr/lib/sendmail has been turned into a symbolic link, this script fails to stop Exim because it uses the command ps -e and greps the output for the text “sendmail”; this is not present because the actual program name (that is, “exim”) is given by the ps command with these options. A solution is to replace the line that finds the process id with something like
to obtain the daemon’s pid directly from the file that Exim saves it in.
Note, however, that stopping the daemon does not “stop Exim”. Messages can still be received from local processes, and if automatic delivery is configured (the normal case), deliveries will still occur.