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Content-type: text/html; charset=UTF-8 Man page of PIPE

PIPE

Section: Linux Programmer's Manual (2)
Updated: 2017-11-26
Index Return to Main Contents
 

NAME

pipe, pipe2 - create pipe  

SYNOPSIS

#include <unistd.h>

int pipe(int pipefd[2]);

#define _GNU_SOURCE             /* See feature_test_macros(7) */
#include <fcntl.h>              /* Obtain O_* constant definitions */
#include <unistd.h>

int pipe2(int pipefd[2], int flags);
 

DESCRIPTION

pipe() creates a pipe, a unidirectional data channel that can be used for interprocess communication. The array pipefd is used to return two file descriptors referring to the ends of the pipe. pipefd[0] refers to the read end of the pipe. pipefd[1] refers to the write end of the pipe. Data written to the write end of the pipe is buffered by the kernel until it is read from the read end of the pipe. For further details, see pipe(7).

If flags is 0, then pipe2() is the same as pipe(). The following values can be bitwise ORed in flags to obtain different behavior:

O_CLOEXEC
Set the close-on-exec (FD_CLOEXEC) flag on the two new file descriptors. See the description of the same flag in open(2) for reasons why this may be useful.
O_DIRECT (since Linux 3.4)
Create a pipe that performs I/O in "packet" mode. Each write(2) to the pipe is dealt with as a separate packet, and read(2)s from the pipe will read one packet at a time. Note the following points:
*
Writes of greater than PIPE_BUF bytes (see pipe(7)) will be split into multiple packets. The constant PIPE_BUF is defined in <limits.h>.
*
If a read(2) specifies a buffer size that is smaller than the next packet, then the requested number of bytes are read, and the excess bytes in the packet are discarded. Specifying a buffer size of PIPE_BUF will be sufficient to read the largest possible packets (see the previous point).
*
Zero-length packets are not supported. (A read(2) that specifies a buffer size of zero is a no-op, and returns 0.)
Older kernels that do not support this flag will indicate this via an EINVAL error.
Since Linux 4.5, it is possible to change the O_DIRECT setting of a pipe file descriptor using fcntl(2).
O_NONBLOCK
Set the O_NONBLOCK file status flag on the two new open file descriptions. Using this flag saves extra calls to fcntl(2) to achieve the same result.
 

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

On Linux (and other systems), pipe() does not modify pipefd on failure. A requirement standardizing this behavior was added in POSIX.1-2016. The Linux-specific pipe2() system call likewise does not modify pipefd on failure.  

ERRORS

EFAULT
pipefd is not valid.
EINVAL
(pipe2()) Invalid value in flags.
EMFILE
The per-process limit on the number of open file descriptors has been reached.
ENFILE
The system-wide limit on the total number of open files has been reached.
ENFILE
The user hard limit on memory that can be allocated for pipes has been reached and the caller is not privileged; see pipe(7).
 

VERSIONS

pipe2() was added to Linux in version 2.6.27; glibc support is available starting with version 2.9.  

CONFORMING TO

pipe(): POSIX.1-2001, POSIX.1-2008.

pipe2() is Linux-specific.  

EXAMPLE

The following program creates a pipe, and then fork(2)s to create a child process; the child inherits a duplicate set of file descriptors that refer to the same pipe. After the fork(2), each process closes the file descriptors that it doesn't need for the pipe (see pipe(7)). The parent then writes the string contained in the program's command-line argument to the pipe, and the child reads this string a byte at a time from the pipe and echoes it on standard output.  

Program source

#include <sys/types.h> #include <sys/wait.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <string.h>

int main(int argc, char *argv[]) {
    int pipefd[2];
    pid_t cpid;
    char buf;


    if (argc != 2) {
        fprintf(stderr, "Usage: %s <string>\n", argv[0]);
        exit(EXIT_FAILURE);
    }


    if (pipe(pipefd) == -1) {
        perror("pipe");
        exit(EXIT_FAILURE);
    }


    cpid = fork();
    if (cpid == -1) {
        perror("fork");
        exit(EXIT_FAILURE);
    }


    if (cpid == 0) {    /* Child reads from pipe */
        close(pipefd[1]);          /* Close unused write end */


        while (read(pipefd[0], &buf, 1) > 0)
            write(STDOUT_FILENO, &buf, 1);


        write(STDOUT_FILENO, "\n", 1);
        close(pipefd[0]);
        _exit(EXIT_SUCCESS);


    } else {            /* Parent writes argv[1] to pipe */
        close(pipefd[0]);          /* Close unused read end */
        write(pipefd[1], argv[1], strlen(argv[1]));
        close(pipefd[1]);          /* Reader will see EOF */
        wait(NULL);                /* Wait for child */
        exit(EXIT_SUCCESS);
    } }  

SEE ALSO

fork(2), read(2), socketpair(2), splice(2), tee(2), vmsplice(2), write(2), popen(3), pipe(7)  

COLOPHON

This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
VERSIONS
CONFORMING TO
EXAMPLE
Program source
SEE ALSO
COLOPHON
This document was created by man2html, using the manual pages.
Time: 04:45:35 GMT, September 16, 2022 Content-type: text/html; charset=UTF-8 Man page of PIPE

PIPE

Section: Linux Programmer's Manual (7)
Updated: 2017-09-15
Index Return to Main Contents
 

NAME

pipe - overview of pipes and FIFOs  

DESCRIPTION

Pipes and FIFOs (also known as named pipes) provide a unidirectional interprocess communication channel. A pipe has a read end and a write end. Data written to the write end of a pipe can be read from the read end of the pipe.

A pipe is created using pipe(2), which creates a new pipe and returns two file descriptors, one referring to the read end of the pipe, the other referring to the write end. Pipes can be used to create a communication channel between related processes; see pipe(2) for an example.

A FIFO (short for First In First Out) has a name within the filesystem (created using mkfifo(3)), and is opened using open(2). Any process may open a FIFO, assuming the file permissions allow it. The read end is opened using the O_RDONLY flag; the write end is opened using the O_WRONLY flag. See fifo(7) for further details. Note: although FIFOs have a pathname in the filesystem, I/O on FIFOs does not involve operations on the underlying device (if there is one).  

I/O on pipes and FIFOs

The only difference between pipes and FIFOs is the manner in which they are created and opened. Once these tasks have been accomplished, I/O on pipes and FIFOs has exactly the same semantics.

If a process attempts to read from an empty pipe, then read(2) will block until data is available. If a process attempts to write to a full pipe (see below), then write(2) blocks until sufficient data has been read from the pipe to allow the write to complete. Nonblocking I/O is possible by using the fcntl(2) F_SETFL operation to enable the O_NONBLOCK open file status flag.

The communication channel provided by a pipe is a byte stream: there is no concept of message boundaries.

If all file descriptors referring to the write end of a pipe have been closed, then an attempt to read(2) from the pipe will see end-of-file (read(2) will return 0). If all file descriptors referring to the read end of a pipe have been closed, then a write(2) will cause a SIGPIPE signal to be generated for the calling process. If the calling process is ignoring this signal, then write(2) fails with the error EPIPE. An application that uses pipe(2) and fork(2) should use suitable close(2) calls to close unnecessary duplicate file descriptors; this ensures that end-of-file and SIGPIPE/EPIPE are delivered when appropriate.

It is not possible to apply lseek(2) to a pipe.  

Pipe capacity

A pipe has a limited capacity. If the pipe is full, then a write(2) will block or fail, depending on whether the O_NONBLOCK flag is set (see below). Different implementations have different limits for the pipe capacity. Applications should not rely on a particular capacity: an application should be designed so that a reading process consumes data as soon as it is available, so that a writing process does not remain blocked.

In Linux versions before 2.6.11, the capacity of a pipe was the same as the system page size (e.g., 4096 bytes on i386). Since Linux 2.6.11, the pipe capacity is 16 pages (i.e., 65,536 bytes in a system with a page size of 4096 bytes). Since Linux 2.6.35, the default pipe capacity is 16 pages, but the capacity can be queried and set using the fcntl(2) F_GETPIPE_SZ and F_SETPIPE_SZ operations. See fcntl(2) for more information.

The following ioctl(2) operation, which can be applied to a file descriptor that refers to either end of a pipe, places a count of the number of unread bytes in the pipe in the int buffer pointed to by the final argument of the call:


    ioctl(fd, FIONREAD, &nbytes);

The FIONREAD operation is not specified in any standard, but is provided on many implementations.  

/proc files

On Linux, the following files control how much memory can be used for pipes:
/proc/sys/fs/pipe-max-pages (only in Linux 2.6.34)
An upper limit, in pages, on the capacity that an unprivileged user (one without the CAP_SYS_RESOURCE capability) can set for a pipe.
The default value for this limit is 16 times the default pipe capacity (see above); the lower limit is two pages.
This interface was removed in Linux 2.6.35, in favor of /proc/sys/fs/pipe-max-size.
/proc/sys/fs/pipe-max-size (since Linux 2.6.35)
The maximum size (in bytes) of individual pipes that can be set by users without the CAP_SYS_RESOURCE capability. The value assigned to this file may be rounded upward, to reflect the value actually employed for a convenient implementation. To determine the rounded-up value, display the contents of this file after assigning a value to it.
The default value for this file is 1048576 (1 MiB). The minimum value that can be assigned to this file is the system page size. Attempts to set a limit less than the page size cause write(2) to fail with the error EINVAL.
Since Linux 4.9, the value on this file also acts as a ceiling on the default capacity of a new pipe or newly opened FIFO.
/proc/sys/fs/pipe-user-pages-hard (since Linux 4.5)
The hard limit on the total size (in pages) of all pipes created or set by a single unprivileged user (i.e., one with neither the CAP_SYS_RESOURCE nor the CAP_SYS_ADMIN capability). So long as the total number of pages allocated to pipe buffers for this user is at this limit, attempts to create new pipes will be denied, and attempts to increase a pipe's capacity will be denied.
When the value of this limit is zero (which is the default), no hard limit is applied.
/proc/sys/fs/pipe-user-pages-soft (since Linux 4.5)
The soft limit on the total size (in pages) of all pipes created or set by a single unprivileged user (i.e., one with neither the CAP_SYS_RESOURCE nor the CAP_SYS_ADMIN capability). So long as the total number of pages allocated to pipe buffers for this user is at this limit, individual pipes created by a user will be limited to one page, and attempts to increase a pipe's capacity will be denied.
When the value of this limit is zero, no soft limit is applied. The default value for this file is 16384, which permits creating up to 1024 pipes with the default capacity.

Before Linux 4.9, some bugs affected the handling of the pipe-user-pages-soft and pipe-user-pages-hard limits; see BUGS.  

PIPE_BUF

POSIX.1 says that write(2)s of less than PIPE_BUF bytes must be atomic: the output data is written to the pipe as a contiguous sequence. Writes of more than PIPE_BUF bytes may be nonatomic: the kernel may interleave the data with data written by other processes. POSIX.1 requires PIPE_BUF to be at least 512 bytes. (On Linux, PIPE_BUF is 4096 bytes.) The precise semantics depend on whether the file descriptor is nonblocking (O_NONBLOCK), whether there are multiple writers to the pipe, and on n, the number of bytes to be written:
O_NONBLOCK disabled, n <= PIPE_BUF
All n bytes are written atomically; write(2) may block if there is not room for n bytes to be written immediately
O_NONBLOCK enabled, n <= PIPE_BUF
If there is room to write n bytes to the pipe, then write(2) succeeds immediately, writing all n bytes; otherwise write(2) fails, with errno set to EAGAIN.
O_NONBLOCK disabled, n > PIPE_BUF
The write is nonatomic: the data given to write(2) may be interleaved with write(2)s by other process; the write(2) blocks until n bytes have been written.
O_NONBLOCK enabled, n > PIPE_BUF
If the pipe is full, then write(2) fails, with errno set to EAGAIN. Otherwise, from 1 to n bytes may be written (i.e., a "partial write" may occur; the caller should check the return value from write(2) to see how many bytes were actually written), and these bytes may be interleaved with writes by other processes.
 

Open file status flags

The only open file status flags that can be meaningfully applied to a pipe or FIFO are O_NONBLOCK and O_ASYNC.

Setting the O_ASYNC flag for the read end of a pipe causes a signal (SIGIO by default) to be generated when new input becomes available on the pipe. The target for delivery of signals must be set using the fcntl(2) F_SETOWN command. On Linux, O_ASYNC is supported for pipes and FIFOs only since kernel 2.6.  

Portability notes

On some systems (but not Linux), pipes are bidirectional: data can be transmitted in both directions between the pipe ends. POSIX.1 requires only unidirectional pipes. Portable applications should avoid reliance on bidirectional pipe semantics.  

BUGS

Before Linux 4.9, some bugs affected the handling of the pipe-user-pages-soft and pipe-user-pages-hard limits when using the fcntl(2) F_SETPIPE_SZ operation to change a pipe's capacity:
(1)
When increasing the pipe capacity, the checks against the soft and hard limits were made against existing consumption, and excluded the memory required for the increased pipe capacity. The new increase in pipe capacity could then push the total memory used by the user for pipes (possibly far) over a limit. (This could also trigger the problem described next.)
Starting with Linux 4.9, the limit checking includes the memory required for the new pipe capacity.
(2)
The limit checks were performed even when the new pipe capacity was less than the existing pipe capacity. This could lead to problems if a user set a large pipe capacity, and then the limits were lowered, with the result that the user could no longer decrease the pipe capacity.
Starting with Linux 4.9, checks against the limits are performed only when increasing a pipe's capacity; an unprivileged user can always decrease a pipe's capacity.
(3)
The accounting and checking against the limits were done as follows:
(a)
Test whether the user has exceeded the limit.
(b)
Make the new pipe buffer allocation.
(c)
Account new allocation against the limits.
This was racey. Multiple processes could pass point (a) simultaneously, and then allocate pipe buffers that were accounted for only in step (c), with the result that the user's pipe buffer allocation could be pushed over the limit.
Starting with Linux 4.9, the accounting step is performed before doing the allocation, and the operation fails if the limit would be exceeded.

Before Linux 4.9, bugs similar to points (1) and (3) could also occur when the kernel allocated memory for a new pipe buffer; that is, when calling pipe(2) and when opening a previously unopened FIFO.  

SEE ALSO

mkfifo(1), dup(2), fcntl(2), open(2), pipe(2), poll(2), select(2), socketpair(2), splice(2), stat(2), tee(2), vmsplice(2), mkfifo(3), epoll(7), fifo(7)  

COLOPHON

This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

 

Index

NAME
DESCRIPTION
I/O on pipes and FIFOs
Pipe capacity
/proc files
PIPE_BUF
Open file status flags
Portability notes
BUGS
SEE ALSO
COLOPHON
This document was created by man2html, using the manual pages.
Time: 04:45:57 GMT, September 16, 2022 Content-type: text/html; charset=UTF-8 Man page of PIPE

PIPE

Section: Misc. Reference Manual Pages (8postfix)
Index Return to Main Contents
 

NAME

pipe - Postfix delivery to external command  

SYNOPSIS

pipe [generic Postfix daemon options] command_attributes...
 

DESCRIPTION

The pipe(8) daemon processes requests from the Postfix queue manager to deliver messages to external commands. This program expects to be run from the master(8) process manager.

Message attributes such as sender address, recipient address and next-hop host name can be specified as command-line macros that are expanded before the external command is executed.

The pipe(8) daemon updates queue files and marks recipients as finished, or it informs the queue manager that delivery should be tried again at a later time. Delivery status reports are sent to the bounce(8), defer(8) or trace(8) daemon as appropriate.  

SINGLE-RECIPIENT DELIVERY



Some destinations cannot handle more than one recipient per
delivery request. Examples are pagers or fax machines.
In addition, multi-recipient delivery is undesirable when
prepending a Delivered-to: or X-Original-To:
message header.


To prevent Postfix from sending multiple recipients per delivery
request, specify



    transport_destination_recipient_limit = 1





in the Postfix main.cf file, where transport
is the name in the first column of the Postfix master.cf
entry for the pipe-based delivery transport.
 

COMMAND ATTRIBUTE SYNTAX






The external command attributes are given in the master.cf
file at the end of a service definition.  The syntax is as follows:



chroot=pathname (optional)

Change the process root directory and working directory to
the named directory. This happens before switching to the
privileges specified with the user attribute, and
before executing the optional directory=pathname
directive. Delivery is deferred in case of failure.


This feature is available as of Postfix 2.3.

directory=pathname (optional)

Change to the named directory before executing the external command.
The directory must be accessible for the user specified with the
user attribute (see below).
The default working directory is $queue_directory.
Delivery is deferred in case of failure.


This feature is available as of Postfix 2.2.

eol=string (optional, default: \n)

The output record delimiter. Typically one would use either
\r\n or \n. The usual C-style backslash escape
sequences are recognized: \a \b \f \n \r \t \v
\ddd (up to three octal digits) and \\.

flags=BDFORXhqu.> (optional)

Optional message processing flags. By default, a message is
copied unchanged.





B

Append a blank line at the end of each message. This is required
by some mail user agents that recognize "From " lines only
when preceded by a blank line.

D

Prepend a "Delivered-To: recipient" message header with the
envelope recipient address. Note: for this to work, the
transport_destination_recipient_limit must be 1
(see SINGLE-RECIPIENT DELIVERY above for details).


The D flag also enforces loop detection (Postfix 2.5 and later):
if a message already contains a Delivered-To: header
with the same recipient address, then the message is
returned as undeliverable. The address comparison is case
insensitive.


This feature is available as of Postfix 2.0.

F

Prepend a "From sender time_stamp" envelope header to
the message content.
This is expected by, for example, UUCP software.

O

Prepend an "X-Original-To: recipient" message header
with the recipient address as given to Postfix. Note: for this to
work, the transport_destination_recipient_limit must be 1
(see SINGLE-RECIPIENT DELIVERY above for details).


This feature is available as of Postfix 2.0.

R

Prepend a Return-Path: message header with the envelope sender
address.

X

Indicate that the external command performs final delivery.
This flag affects the status reported in "success" DSN
(delivery status notification) messages, and changes it
from "relayed" into "delivered".


This feature is available as of Postfix 2.5.

h

Fold the command-line $original_recipient and
$recipient address domain part
(text to the right of the right-most @ character) to
lower case; fold the entire command-line $domain and
$nexthop host or domain information to lower case.
This is recommended for delivery via UUCP.

q

Quote white space and other special characters in the command-line
$sender, $original_recipient and $recipient
address localparts (text to the
left of the right-most @ character), according to an 8-bit
transparent version of RFC 822.
This is recommended for delivery via UUCP or BSMTP.


The result is compatible with the address parsing of command-line
recipients by the Postfix sendmail(1) mail submission command.


The q flag affects only entire addresses, not the partial
address information from the $user, $extension or
$mailbox command-line macros.

u

Fold the command-line $original_recipient and
$recipient address localpart (text to
the left of the right-most @ character) to lower case.
This is recommended for delivery via UUCP.

.

Prepend "." to lines starting with ".". This is needed
by, for example, BSMTP software.

>

Prepend ">" to lines starting with "From ". This is expected
by, for example, UUCP software.






null_sender=replacement (default: MAILER-DAEMON)

Replace the null sender address (typically used for delivery
status notifications) with the specified text
when expanding the $sender command-line macro, and
when generating a From_ or Return-Path: message header.


If the null sender replacement text is a non-empty string
then it is affected by the q flag for address quoting
in command-line arguments.


The null sender replacement text may be empty; this form
is recommended for content filters that feed mail back into
Postfix. The empty sender address is not affected by the
q flag for address quoting in command-line arguments.


Caution: a null sender address is easily mis-parsed by
naive software. For example, when the pipe(8) daemon
executes a command such as:



    Wrong: command -f$sender -- $recipient





the command will mis-parse the -f option value when the
sender address is a null string.  For correct parsing,
specify $sender as an argument by itself:



    Right: command -f $sender -- $recipient





This feature is available as of Postfix 2.3.

size=size_limit (optional)

Don't deliver messages that exceed this size limit (in
bytes); return them to the sender instead.

user=username (required)


user=username:groupname

Execute the external command with the user ID and group ID of the
specified username.  The software refuses to execute
commands with root privileges, or with the privileges of the
mail system owner. If groupname is specified, the
corresponding group ID is used instead of the group ID of
username.

argv=command... (required)

The command to be executed. This must be specified as the
last command attribute.
The command is executed directly, i.e. without interpretation of
shell meta characters by a shell command interpreter.


Specify "{" and "}" around command arguments that contain
whitespace (Postfix 3.0 and later). Whitespace
after "{" and before "}" is ignored.


In the command argument vector, the following macros are recognized
and replaced with corresponding information from the Postfix queue
manager delivery request.


In addition to the form ${name}, the forms $name and
the deprecated form $(name) are also recognized.
Specify $$ where a single $ is wanted.





${client_address}

This macro expands to the remote client network address.


This feature is available as of Postfix 2.2.

${client_helo}

This macro expands to the remote client HELO command parameter.


This feature is available as of Postfix 2.2.

${client_hostname}

This macro expands to the remote client hostname.


This feature is available as of Postfix 2.2.

${client_port}

This macro expands to the remote client TCP port number.


This feature is available as of Postfix 2.5.

${client_protocol}

This macro expands to the remote client protocol.


This feature is available as of Postfix 2.2.

${domain}

This macro expands to the domain portion of the recipient
address.  For example, with an address user+foo@domain
the domain is domain.


This information is modified by the h flag for case folding.


This feature is available as of Postfix 2.5.

${extension}

This macro expands to the extension part of a recipient address.
For example, with an address user+foo@domain the extension is
foo.


A command-line argument that contains ${extension} expands
into as many command-line arguments as there are recipients.


This information is modified by the u flag for case folding.

${mailbox}

This macro expands to the complete local part of a recipient address.
For example, with an address user+foo@domain the mailbox is
user+foo.


A command-line argument that contains ${mailbox}
expands to as many command-line arguments as there are recipients.


This information is modified by the u flag for case folding.

${nexthop}

This macro expands to the next-hop hostname.


This information is modified by the h flag for case folding.

${original_recipient}

This macro expands to the complete recipient address before any
address rewriting or aliasing.


A command-line argument that contains
${original_recipient} expands to as many
command-line arguments as there are recipients.


This information is modified by the hqu flags for quoting
and case folding.


This feature is available as of Postfix 2.5.

${queue_id}

This macro expands to the queue id.


This feature is available as of Postfix 2.11.

${recipient}

This macro expands to the complete recipient address.


A command-line argument that contains ${recipient}
expands to as many command-line arguments as there are recipients.


This information is modified by the hqu flags for quoting
and case folding.

${sasl_method}

This macro expands to the name of the SASL authentication
mechanism in the AUTH command when the Postfix SMTP server
received the message.


This feature is available as of Postfix 2.2.

${sasl_sender}

This macro expands to the SASL sender name (i.e. the original
submitter as per RFC 4954) in the MAIL FROM command when
the Postfix SMTP server received the message.


This feature is available as of Postfix 2.2.

${sasl_username}

This macro expands to the SASL user name in the AUTH command
when the Postfix SMTP server received the message.


This feature is available as of Postfix 2.2.

${sender}

This macro expands to the envelope sender address. By default,
the null sender address expands to MAILER-DAEMON; this can
be changed with the null_sender attribute, as described
above.


This information is modified by the q flag for quoting.

${size}

This macro expands to Postfix's idea of the message size, which
is an approximation of the size of the message as delivered.

${user}

This macro expands to the username part of a recipient address.
For example, with an address user+foo@domain the username
part is user.


A command-line argument that contains ${user} expands
into as many command-line arguments as there are recipients.


This information is modified by the u flag for case folding.







 

STANDARDS




RFC 3463 (Enhanced status codes)

 

DIAGNOSTICS




Command exit status codes are expected to
follow the conventions defined in <sysexits.h>.
Exit status 0 means normal successful completion.


In the case of a non-zero exit status, a limited amount of
command output is logged, and reported in a delivery status
notification.  When the output begins with a 4.X.X or 5.X.X
enhanced status code, the status code takes precedence over
the non-zero exit status (Postfix version 2.3 and later).


After successful delivery (zero exit status) a limited
amount of command output is logged, and reported in "success"
delivery status notifications (Postfix 3.0 and later).
This command output is not examined for the presence of an
enhanced status code.


Problems and transactions are logged to syslogd(8).
Corrupted message files are marked so that the queue manager
can move them to the corrupt queue for further inspection.
 

SECURITY







This program needs a dual personality 1) to access the private
Postfix queue and IPC mechanisms, and 2) to execute external
commands as the specified user. It is therefore security sensitive.
 

CONFIGURATION PARAMETERS






Changes to main.cf are picked up automatically as pipe(8)
processes run for only a limited amount of time. Use the command
"postfix reload" to speed up a change.


The text below provides only a parameter summary. See
postconf(5) for more details including examples.
 

RESOURCE AND RATE CONTROLS






In the text below, transport is the first field in a
master.cf entry.



transport_time_limit ($command_time_limit)

A transport-specific override for the command_time_limit parameter
value, where transport is the master.cf name of the message
delivery transport.





Implemented in the qmgr(8) daemon:



transport_destination_concurrency_limit ($default_destination_concurrency_limit)

A transport-specific override for the
default_destination_concurrency_limit parameter value, where
transport is the master.cf name of the message delivery
transport.

transport_destination_recipient_limit ($default_destination_recipient_limit)

A transport-specific override for the
default_destination_recipient_limit parameter value, where
transport is the master.cf name of the message delivery
transport.


 

MISCELLANEOUS CONTROLS









config_directory (see 'postconf -d' output)

The default location of the Postfix main.cf and master.cf
configuration files.

daemon_timeout (18000s)

How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.

delay_logging_resolution_limit (2)

The maximal number of digits after the decimal point when logging
sub-second delay values.

export_environment (see 'postconf -d' output)

The list of environment variables that a Postfix process will export
to non-Postfix processes.

ipc_timeout (3600s)

The time limit for sending or receiving information over an internal
communication channel.

mail_owner (postfix)

The UNIX system account that owns the Postfix queue and most Postfix
daemon processes.

max_idle (100s)

The maximum amount of time that an idle Postfix daemon process waits
for an incoming connection before terminating voluntarily.

max_use (100)

The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily.

process_id (read-only)

The process ID of a Postfix command or daemon process.

process_name (read-only)

The process name of a Postfix command or daemon process.

queue_directory (see 'postconf -d' output)

The location of the Postfix top-level queue directory.

recipient_delimiter (empty)

The set of characters that can separate a user name from its
extension (example: user+foo), or a .forward file name from its
extension (example: .forward+foo).

syslog_facility (mail)

The syslog facility of Postfix logging.

syslog_name (see 'postconf -d' output)

A prefix that is prepended to the process name in syslog
records, so that, for example, "smtpd" becomes "prefix/smtpd".





Available in Postfix version 3.0 and later:



pipe_delivery_status_filter ($default_delivery_status_filter)

Optional filter for the pipe(8) delivery agent to change the
delivery status code or explanatory text of successful or unsuccessful
deliveries.





Available in Postfix version 3.3 and later:



enable_original_recipient (yes)

Enable support for the original recipient address after an
address is rewritten to a different address (for example with
aliasing or with canonical mapping).

service_name (read-only)

The master.cf service name of a Postfix daemon process.


 

SEE ALSO




qmgr(8), queue manager
bounce(8), delivery status reports
postconf(5), configuration parameters
master(5), generic daemon options
master(8), process manager
syslogd(8), system logging

 

LICENSE






The Secure Mailer license must be distributed with this software.
 

AUTHOR(S)




Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA

Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA





 
Index




NAME


SYNOPSIS


DESCRIPTION


SINGLE-RECIPIENT DELIVERY


COMMAND ATTRIBUTE SYNTAX


STANDARDS


DIAGNOSTICS


SECURITY


CONFIGURATION PARAMETERS


RESOURCE AND RATE CONTROLS


MISCELLANEOUS CONTROLS


SEE ALSO


LICENSE


AUTHOR(S)





This document was created by
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Time: 04:46:02 GMT, September 16, 2022








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