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diff --git a/README_FILES/DATABASE_README b/README_FILES/DATABASE_README new file mode 100644 index 0000000..99e10a7 --- /dev/null +++ b/README_FILES/DATABASE_README @@ -0,0 +1,325 @@ +PPoossttffiixx LLooookkuupp TTaabbllee OOvveerrvviieeww + +------------------------------------------------------------------------------- + +OOvveerrvviieeww + +This document covers the following topics: + + * The Postfix lookup table model + * Postfix lists versus tables + * Preparing Postfix for LDAP or SQL lookups + * Maintaining Postfix lookup table files + * Updating Berkeley DB files safely + * Postfix lookup table types + +TThhee PPoossttffiixx llooookkuupp ttaabbllee mmooddeell + +Postfix uses lookup tables to store and look up information for access control, +address rewriting and even for content filtering. All Postfix lookup tables are +specified as "type:table", where "type" is one of the database types described +under "Postfix lookup table types" at the end of this document, and where +"table" is the lookup table name. The Postfix documentation uses the terms +"database" and "lookup table" for the same thing. + +Examples of lookup tables that appear often in the Postfix documentation: + + /etc/postfix/main.cf: + alias_maps = hash:/etc/postfix/aliases (local aliasing) + header_checks = regexp:/etc/postfix/header_checks (content filtering) + transport_maps = hash:/etc/postfix/transport (routing table) + virtual_alias_maps = hash:/etc/postfix/virtual (address rewriting) + +All Postfix lookup tables store information as (key, value) pairs. This +interface may seem simplistic at first, but it turns out to be very powerful. +The (key, value) query interface completely hides the complexities of LDAP or +SQL from Postfix. This is a good example of connecting complex systems with +simple interfaces. + +Benefits of the Postfix (key, value) query interface: + + * You can implement Postfix lookup tables first with local Berkeley DB files + and then switch to LDAP or MySQL without any impact on the Postfix + configuration itself, as described under "Preparing Postfix for LDAP or SQL + lookups" below. + * You can use Berkeley DB files with fixed lookup strings for simple address + rewriting operations and you can use regular expression tables for the more + complicated work. In other words, you don't have to put everything into the + same table. + +PPoossttffiixx lliissttss vveerrssuuss ttaabblleess + +Most Postfix lookup tables are used to look up information. Examples are +address rewriting (the lookup string is the old address, and the result is the +new address) or access control (the lookup string is the client, sender or +recipient, and the result is an action such as "reject"). + +With some tables, however, Postfix needs to know only if the lookup key exists. +Any non-empty lookup result value may be used here: the lookup result is not +used. Examples are the local_recipient_maps that determine what local +recipients Postfix accepts in mail from the network, the mydestination +parameter that specifies what domains Postfix delivers locally, or the +mynetworks parameter that specifies the IP addresses of trusted clients or +client networks. Technically, these are lists, not tables. Despite the +difference, Postfix lists are described here because they use the same +underlying infrastructure as Postfix lookup tables. + +PPrreeppaarriinngg PPoossttffiixx ffoorr LLDDAAPP oorr SSQQLL llooookkuuppss + +LDAP and SQL are complex systems. Trying to set up both Postfix and LDAP or SQL +at the same time is definitely not a good idea. You can save yourself a lot of +time by implementing Postfix first with local files such as Berkeley DB. Local +files have few surprises, and are easy to debug with the postmap(1) command: + + % ppoossttmmaapp --qq iinnffoo@@eexxaammppllee..ccoomm hhaasshh:://eettcc//ppoossttffiixx//vviirrttuuaall + +Once you have local files working properly you can follow the instructions in +ldap_table(5), mysql_table(5), pgsql_table(5) or sqlite_table(5) and replace +local file lookups with LDAP or SQL lookups. When you do this, you should use +the postmap(1) command again, to verify that database lookups still produce the +exact same results as local file lookup: + + % ppoossttmmaapp --qq iinnffoo@@eexxaammppllee..ccoomm llddaapp:://eettcc//ppoossttffiixx//vviirrttuuaall..ccff + +Be sure to exercise all the partial address or parent domain queries that are +documented under "table search order" in the relevant manual page: access(5), +canonical(5), virtual(5), transport(5), or under the relevant configuration +parameter: mynetworks, relay_domains, parent_domain_matches_subdomains. + +MMaaiinnttaaiinniinngg PPoossttffiixx llooookkuupp ttaabbllee ffiilleess + +When you make changes to a database while the mail system is running, it would +be desirable if Postfix avoids reading information while that information is +being changed. It would also be nice if you can change a database without +having to execute "postfix reload", in order to force Postfix to use the new +information. Each time you do "postfix reload" Postfix loses a lot of +performance. + + * If you change a network database such as LDAP, NIS or SQL, there is no need + to execute "postfix reload". The LDAP, NIS or SQL server takes care of + read/write access conflicts and gives the new data to Postfix once that + data is available. + + * If you change a regexp:, pcre:, cidr: or texthash: file then Postfix may + not pick up the file changes immediately. This is because a Postfix process + reads the entire file into memory once and never examines the file again. + + o If the file is used by a short-running process such as smtpd(8), + cleanup(8) or local(8), there is no need to execute "postfix reload" + after making a change. + + o If the file is being used by a long-running process such as trivial- + rewrite(8) on a busy server it may be necessary to execute "postfix + reload". + + * If you change a local file based database such as DBM or Berkeley DB, there + is no need to execute "postfix reload". Postfix uses file locking to avoid + read/write access conflicts, and whenever a Postfix daemon process notices + that a file has changed it will terminate before handling the next client + request, so that a new process can initialize with the new database. + +UUppddaattiinngg BBeerrkkeelleeyy DDBB ffiilleess ssaaffeellyy + +Postfix uses file locking to avoid access conflicts while updating Berkeley DB +or other local database files. This used to be safe, but as Berkeley DB has +evolved to use more aggressive caching, file locking may no longer be +sufficient. + +Furthermore, file locking would not prevent problems when the update fails +because the disk is full or something else causes a database update to fail. In +particular, commands such as postmap(1) or postalias(1) overwrite existing +files. If the overwrite fails in the middle then you have no usable database, +and Postfix will stop working. This is not an issue with the CDB database type +available with Postfix 2.2 and later: CDB creates a new file, and renames the +file upon successful completion. + +With Berkeley DB and other "one file" databases, it is possible to add some +extra robustness by using "mv" to REPLACE an existing database file instead of +overwriting it: + + # ppoossttmmaapp aacccceessss..iinn &&&& mmvv aacccceessss..iinn..ddbb aacccceessss..ddbb + +This converts the input file "access.in" into the output file "access.in.db", +and replaces the file "access.db" only when the postmap(1) command was +successful. Of course typing such commands becomes boring quickly, and this is +why people use "make" instead, as shown below. User input is shown in bold +font. + + # ccaatt MMaakkeeffiillee + all: aliases.db access.db virtual.db ...etcetera... + + # Note 1: commands are specified after a TAB character. + # Note 2: use postalias(1) for local aliases, postmap(1) for the rest. + aliases.db: aliases.in + postalias aliases.in + mv aliases.in.db aliases.db + + access.db: access.in + postmap access.in + mv access.in.db access.db + + virtual.db: virtual.in + postmap virtual.in + mv virtual.in.db virtual.db + + ...etcetera... + # vvii aacccceessss..iinn + ...editing session not shown... + # mmaakkee + postmap access.in + mv access.in.db access.db + # + +The "make" command updates only the files that have changed. In case of error, +the "make" command will stop and will not invoke the "mv" command, so that +Postfix will keep using the existing database file as if nothing happened. + +PPoossttffiixx llooookkuupp ttaabbllee ttyyppeess + +To find out what database types your Postfix system supports, use the "ppoossttccoonnff +--mm" command. Here is a list of database types that are often supported: + + bbttrreeee + A sorted, balanced tree structure. This is available only on systems + with support for Berkeley DB databases. Database files are created with + the postmap(1) or postalias(1) command. The lookup table name as used + in "btree:table" is the database file name without the ".db" suffix. + ccddbb + A read-optimized structure with no support for incremental updates. + Database files are created with the postmap(1) or postalias(1) command. + The lookup table name as used in "cdb:table" is the database file name + without the ".cdb" suffix. This feature is available with Postfix 2.2 + and later. + cciiddrr + A table that associates values with Classless Inter-Domain Routing + (CIDR) patterns. The table format is described in cidr_table(5). + ddbbmm + An indexed file type based on hashing. This is available only on + systems with support for DBM databases. Public database files are + created with the postmap(1) or postalias(1) command, and private + databases are maintained by Postfix daemons. The lookup table name as + used in "dbm:table" is the database file name without the ".dir" or + ".pag" suffix. + eennvviirroonn + The UNIX process environment array. The lookup key is the variable + name. The lookup table name in "environ:table" is ignored. + ffaaiill + A table that reliably fails all requests. The lookup table name is used + for logging only. This table exists to simplify Postfix error tests. + hhaasshh + An indexed file type based on hashing. This is available only on + systems with support for Berkeley DB databases. Public database files + are created with the postmap(1) or postalias(1) command, and private + databases are maintained by Postfix daemons. The database name as used + in "hash:table" is the database file name without the ".db" suffix. + iinnlliinnee (read-only) + A non-shared, in-memory lookup table. Example: "inline:{ key=value, + { key = text with whitespace or comma }}". Key-value pairs are + separated by whitespace or comma; with a key-value pair inside "{}", + whitespace is ignored after the opening "{", around the "=" between key + and value, and before the closing "}". Inline tables eliminate the need + to create a database file for just a few fixed elements. See also the + static: map type. + iinntteerrnnaall + A non-shared, in-memory hash table. Its content are lost when a process + terminates. + llmmddbb + OpenLDAP LMDB database. This is available only on systems with support + for LMDB databases. Public database files are created with the postmap + (1) or postalias(1) command, and private databases are maintained by + Postfix daemons. The database name as used in "lmdb:table" is the + database file name without the ".lmdb" suffix. See lmdb_table(5) for + details. + llddaapp (read-only) + LDAP database client. Configuration details are given in the ldap_table + (5). + mmeemmccaacchhee + Memcache database client. Configuration details are given in + memcache_table(5). + mmyyssqqll (read-only) + MySQL database client. Configuration details are given in mysql_table + (5). + nneettiinnffoo (read-only) + Netinfo database client. + nniiss (read-only) + NIS database client. + nniisspplluuss (read-only) + NIS+ database client. Configuration details are given in nisplus_table + (5). + ppccrree (read-only) + A lookup table based on Perl Compatible Regular Expressions. The file + format is described in pcre_table(5). The lookup table name as used in + "pcre:table" is the name of the regular expression file. + ppiippeemmaapp (read-only) + A pipeline of lookup tables. Example: "pipemap:{type1:name1, ..., + typen:namen}". Each "pipemap:" query is given to the first table. Each + lookup result becomes the query for the next table in the pipeline, and + the last table produces the final result. When any table lookup + produces no result, the pipeline produces no result. The first and last + characters of the "pipemap:" table name must be "{" and "}". Within + these, individual maps are separated with comma or whitespace. + ppggssqqll (read-only) + PostgreSQL database client. Configuration details are given in + pgsql_table(5). + pprrooxxyy + Postfix proxymap(8) client for shared access to Postfix databases. The + lookup table name syntax is "proxy:type:table". + rraannddmmaapp (read-only) + An in-memory table that performs random selection. Example: "randmap: + {result1. ..., resultn}". Each table query returns a random choice from + the specified results. The first and last characters of the "randmap: + " table name must be "{" and "}". Within these, individual maps are + separated with comma or whitespace. To give a specific result more + weight, specify it multiple times. + rreeggeexxpp (read-only) + A lookup table based on regular expressions. The file format is + described in regexp_table(5). The lookup table name as used in "regexp: + table" is the name of the regular expression file. + ssddbbmm + An indexed file type based on hashing. This is available only on + systems with support for SDBM databases. Public database files are + created with the postmap(1) or postalias(1) command, and private + databases are maintained by Postfix daemons. The lookup table name as + used in "sdbm:table" is the database file name without the ".dir" or + ".pag" suffix. + ssoocckkeettmmaapp (read-only) + Sendmail-style socketmap client. The name of the table is either iinneett: + host:port:name for a TCP/IP server, or uunniixx:pathname:name for a UNIX- + domain server. See socketmap_table(5) for details. + ssqqlliittee (read-only) + SQLite database. Configuration details are given in sqlite_table(5). + ssttaattiicc (read-only) + A table that always returns its name as the lookup result. For example, + "static:foobar" always returns the string "foobar" as lookup result. + Specify "static:{ text with whitespace }" when the result contains + whitespace; this form ignores whitespace after the opening "{" and + before the closing "}". See also the inline: map type. + ttccpp + TCP/IP client. The protocol is described in tcp_table(5). The lookup + table name is "tcp:host:port" where "host" specifies a symbolic + hostname or a numeric IP address, and "port" specifies a symbolic + service name or a numeric port number. + tteexxtthhaasshh (read-only) + A table that produces similar results as hash: files, except that you + don't have to run the postmap(1) command before you can use the file, + and that texthash: does not detect changes after the file is read. The + lookup table name is "texthash:filename", where the file name is taken + literally; no suffix is appended. + uunniioonnmmaapp (read-only) + A table that sends each query to multiple lookup tables and that + concatenates all found results, separated by comma. The table name + syntax is the same as for pipemap tables. + uunniixx (read-only) + A limited view of the UNIX authentication database. The following + tables are implemented: + uunniixx::ppaasssswwdd..bbyynnaammee + The table is the UNIX password database. The key is a login name. + The result is a password file entry in passwd(5) format. + uunniixx::ggrroouupp..bbyynnaammee + The table is the UNIX group database. The key is a group name. The + result is a group file entry in group(5) format. + +Other lookup table types may be available depending on how Postfix was built. +With some Postfix distributions the list is dynamically extensible as support +for lookup tables is dynamically linked into Postfix. + |