This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding Linux
manual page for details of Linux behavior), or the interface may not be
implemented on Linux.
ps — report process status
ps [−aA] [−defl] [−g grouplist] [−G grouplist]
[−n namelist] [−o format]... [−p proclist] [−t termlist]
[−u userlist] [−U userlist]
utility shall write information about processes, subject to having
appropriate privileges to obtain information about those processes.
By default, ps
shall select all processes with the same effective user ID
as the current user and the same controlling terminal as the invoker.
utility shall conform to the Base Definitions volume of
POSIX.1‐2008, Section 12.2
, Utility Syntax Guidelines
The following options shall be supported:
- Write information for all processes associated with
terminals. Implementations may omit session leaders from this list.
- Write information for all processes.
- Write information for all processes, except session
- Write information for all processes. (Equivalent to
- Generate a full listing. (See the STDOUT section for
the contents of a full listing.)
- −g grouplist
- Write information for processes whose session leaders are
given in grouplist. The application shall ensure that the
grouplist is a single argument in the form of a <blank> or
- −G grouplist
- Write information for processes whose real group ID numbers
are given in grouplist. The application shall ensure that the
grouplist is a single argument in the form of a <blank> or
- Generate a long listing. (See STDOUT for the
contents of a long listing.)
- −n namelist
- Specify the name of an alternative system namelist
file in place of the default. The name of the default file and the format
of a namelist file are unspecified.
- −o format
- Write information according to the format specification
given in format. This is fully described in the STDOUT section.
Multiple −o options can be specified; the format
specification shall be interpreted as the <space>-separated
concatenation of all the format option-arguments.
- −p proclist
- Write information for processes whose process ID numbers
are given in proclist. The application shall ensure that the
proclist is a single argument in the form of a <blank> or
- −t termlist
- Write information for processes associated with terminals
given in termlist. The application shall ensure that the
termlist is a single argument in the form of a <blank> or
<comma>-separated list. Terminal identifiers shall be given in an
implementation-defined format. On XSI-conformant systems, they shall be
given in one of two forms: the device's filename (for example,
tty04) or, if the device's filename starts with tty, just
the identifier following the characters tty (for example,
- −u userlist
- Write information for processes whose user ID numbers or
login names are given in userlist. The application shall ensure
that the userlist is a single argument in the form of a
<blank> or <comma>-separated list. In the listing, the
numerical user ID shall be written unless the −f option is
used, in which case the login name shall be written.
- −U userlist
- Write information for processes whose real user ID numbers
or login names are given in userlist. The application shall ensure
that the userlist is a single argument in the form of a
<blank> or <comma>-separated list.
With the exception of −f
, and −o format
, all of the options shown
are used to select processes. If any are specified, the default list shall be
ignored and ps
shall select the processes represented by the inclusive
OR of all the selection-criteria options.
The following environment variables shall affect the execution of ps
- Override the system-selected horizontal display line size,
used to determine the number of text columns to display. See the Base
Definitions volume of POSIX.1‐2008, Chapter 8,
Environment Variables for valid values and results when it is unset
- Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions volume of
POSIX.1‐2008, Section 8.2, Internationalization
Variables the precedence of internationalization variables used to
determine the values of locale categories.)
- If set to a non-empty string value, override the values of
all the other internationalization variables.
- Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
Determine the locale that should be used to affect the format and contents
of diagnostic messages written to standard error and informative messages
written to standard output.
- Determine the format and contents of the date and time
- Determine the location of message catalogs for the
processing of LC_MESSAGES.
- Determine the timezone used to calculate date and time
strings displayed. If TZ is unset or null, an unspecified default
timezone shall be used.
When the −o
option is not specified, the standard output format is
On XSI-conformant systems, the output format shall be as follows. The column
headings and descriptions of the columns in a ps
listing are given
below. The precise meanings of these fields are implementation-defined. The
(below) indicate the option (full
) that shall cause the corresponding heading to appear; all
means that the heading always appears. Note that these two options determine
only what information is provided for a process; they do not determine which
processes are listed.
||Flags (octal and additive) associated with the process.
||The state of the process.
||The user ID number of the process owner; the login name is printed under
the −f option.
||The process ID of the process; it is possible to kill a process if this
datum is known.
||The process ID of the parent process.
||Processor utilization for scheduling.
||The priority of the process; higher numbers mean lower priority.
||Nice value; used in priority computation.
||The address of the process.
||The size in blocks of the core image of the process.
||The event for which the process is waiting or sleeping; if blank, the
process is running.
||Starting time of the process.
||The controlling terminal for the process.
||The cumulative execution time for the process.
||The command name; the full command name and its arguments are written
under the −f option.
A process that has exited and has a parent, but has not yet been waited for by
the parent, shall be marked defunct
Under the option −f
tries to determine the command name
and arguments given when the process was created by examining memory or the
swap area. Failing this, the command name, as it would appear without the
, is written in square brackets.
option allows the output format to be specified under user
The application shall ensure that the format specification is a list of names
presented as a single argument, <blank> or <comma>-separated. Each
variable has a default header. The default header can be overridden by
appending an <equals-sign> and the new text of the header. The rest of
the characters in the argument shall be used as the header text. The fields
specified shall be written in the order specified on the command line, and
should be arranged in columns in the output. The field widths shall be
selected by the system to be at least as wide as the header text (default or
overridden value). If the header text is null, such as −o
=, the field width shall be at least as wide as the default header
text. If all header text fields are null, no header line shall be written.
The following names are recognized in the POSIX locale:
- The real user ID of the process. This shall be the textual
user ID, if it can be obtained and the field width permits, or a decimal
- The effective user ID of the process. This shall be the
textual user ID, if it can be obtained and the field width permits, or a
decimal representation otherwise.
- The real group ID of the process. This shall be the textual
group ID, if it can be obtained and the field width permits, or a decimal
- The effective group ID of the process. This shall be the
textual group ID, if it can be obtained and the field width permits, or a
decimal representation otherwise.
- The decimal value of the process ID.
- The decimal value of the parent process ID.
- The decimal value of the process group ID.
- The ratio of CPU time used recently to CPU time available
in the same period, expressed as a percentage. The meaning of ``recently''
in this context is unspecified. The CPU time available is determined in an
- The size of the process in (virtual) memory in 1024 byte
units as a decimal integer.
- The decimal value of the nice value of the process; see
- In the POSIX locale, the elapsed time since the process was
started, in the form:
shall represent the number of days, hh
the number of
the number of minutes, and ss
the number of seconds.
field shall be a decimal integer. The hh
fields shall be two-digit decimal integers padded on the left with
- In the POSIX locale, the cumulative CPU time of the process
in the form:
, and ss
fields shall be as described
in the etime
- The name of the controlling terminal of the process (if
any) in the same format used by the who utility.
- The name of the command being executed (argv
value) as a string.
- The command with all its arguments as a string. The
implementation may truncate this value to the field width; it is
implementation-defined whether any further truncation occurs. It is
unspecified whether the string represented is a version of the argument
list as it was passed to the command when it started, or is a version of
the arguments as they may have been modified by the application.
Applications cannot depend on being able to modify their argument list and
having that modification be reflected in the output of ps.
Any field need not be meaningful in all implementations. In such a case a
) should be output in place of the field
shall be allowed to contain <blank>
characters; all others shall not. Any implementation-defined variables shall
be specified in the system documentation along with the default header and
indicating whether the field may contain <blank> characters.
The following table specifies the default header to be used in the POSIX locale
corresponding to each format specifier.
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
- Successful completion.
- An error occurred.
The following sections are informative.
Things can change while ps
is running; the snapshot it gives is only true
for an instant, and might not be accurate by the time it is displayed.
format specifier is allowed to produce a truncated version of
the command arguments. In some implementations, this information is no longer
available when the ps
utility is executed.
If the field width is too narrow to display a textual ID, the system may use a
numeric version. Normally, the system would be expected to choose large enough
field widths, but if a large number of fields were selected to write, it might
squeeze fields to their minimum sizes to fit on one line. One way to ensure
adequate width for the textual IDs is to override the default header for a
field to make it larger than most or all user or group names.
There is no special quoting mechanism for header text. The header text is the
rest of the argument. If multiple header changes are needed, multiple
options can be used, such as:
ps −o "user=User Name" −o pid=Process\ ID
On some implementations, especially multi-level secure systems, ps
severely restricted and produce information only about child processes owned
by the user.
ps −o user,pid,ppid=MOM −o args
writes at least the following in the POSIX locale:
USER PID MOM COMMAND
helene 34 12 ps −o uid,pid,ppid=MOM −o args
The contents of the COMMAND
field need not be the same in all
implementations, due to possible truncation.
There is very little commonality between BSD and System V implementations of
. Many options conflict or have subtly different usages. The standard
developers attempted to select a set of options for the base standard that
were useful on a wide range of systems and selected options that either can be
implemented on both BSD and System V-based systems without breaking the
current implementations or where the options are sufficiently similar that any
changes would not be unduly problematic for users or implementors.
It is recognized that on some implementations, especially multi-level secure
may be nearly useless. The default output has therefore
been chosen such that it does not break historical implementations and also is
likely to provide at least some useful information on most systems.
The major change is the addition of the format specification capability. The
motivation for this invention is to provide a mechanism for users to access a
wider range of system information, if the system permits it, in a portable
manner. The fields chosen to appear in this volume of POSIX.1‐2008 were
arrived at after considering what concepts were likely to be both reasonably
useful to the ``average'' user and had a reasonable chance of being
implemented on a wide range of systems. Again it is recognized that not all
systems are able to provide all the information and, conversely, some may wish
to provide more. It is hoped that the approach adopted will be sufficiently
flexible and extensible to accommodate most systems. Implementations may be
expected to introduce new format specifiers.
The default output should consist of a short listing containing the process ID,
terminal name, cumulative execution time, and command name of each process.
The preference of the standard developers would have been to make the format
specification an operand of the ps
command. Unfortunately, BSD usage
At one time a format was included to display the environment array of the
process. This was deleted because there is no portable way to display it.
option is equivalent to the BSD −g
. Because the two systems differed, a mnemonic compromise
option is described with some optional behavior because the
SVID omits session leaders, but BSD does not.
In an early proposal, format specifiers appeared for priority and start time.
The former was not defined adequately in this volume of POSIX.1‐2008
and was removed in deference to the defined nice value; the latter because
elapsed time was considered to be more useful.
In a new BSD version of ps
, a −O
option can be used to
write all of the default information, followed by additional format
specifiers. This was not adopted because the default output is
implementation-defined. Nevertheless, this is a useful option that should be
reserved for that purpose. In the −o
option for the POSIX Shell
and Utilities ps
, the format is the concatenation of each
. Therefore, the user can have an alias or function that
defines the beginning of their desired format and add more fields to the end
of the output in certain cases where that would be useful.
The format of the terminal name is unspecified, but the descriptions of
, and write
require that they all use
the same format.
field indicates that the CPU time available is determined in an
unspecified manner. This is because it is difficult to express an algorithm
that is useful across all possible machine architectures. Historical
counterparts to this value have attempted to show percentage of use in the
recent past, such as the preceding minute. Frequently, these values for all
processes did not add up to 100%. Implementations are encouraged to provide
data in this field to users that will help them identify processes currently
affecting the performance of the system.
The Base Definitions volume of POSIX.1‐2008, Chapter 8
, Section 12.2
, Utility Syntax
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
7, Copyright (C) 2013 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013
Technical Corrigendum 1 applied.) In the event of any discrepancy between this
version and the original IEEE and The Open Group Standard, the original IEEE
and The Open Group Standard is the referee document. The original Standard can
be obtained online at http://www.unix.org/online.html .
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