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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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PS(1P) POSIX Programmer's Manual PS(1P)
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]
The ps 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.
The ps utility shall conform to the Base Definitions volume of
POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
-a Write information for all processes associated with
terminals. Implementations may omit session leaders
from this list.
-A Write information for all processes.
-d Write information for all processes, except session
leaders.
-e Write information for all processes. (Equivalent to
-A.)
-f 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 <comma>-separated list.
-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 <comma>-separated list.
-l 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 <comma>-separated list.
-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, "04").
-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, -l, -n namelist, 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.
None.
Not used.
None.
The following environment variables shall affect the execution of
ps:
COLUMNS 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.1‐2017, Chapter 8, Environment Variables for valid
values and results when it is unset or null.
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base
Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables the precedence of
internationalization variables used to determine the
values of locale categories.)
LC_ALL If set to a non-empty string value, override the values
of all the other internationalization variables.
LC_CTYPE 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).
LC_MESSAGES
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.
LC_TIME Determine the format and contents of the date and time
strings displayed.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
TZ Determine the timezone used to calculate date and time
strings displayed. If TZ is unset or null, an
unspecified default timezone shall be used.
Default.
When the -o option is not specified, the standard output format is
unspecified.
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 letters 'f' and 'l' (below) indicate
the option (full or long) 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.
F (l) Flags (octal and additive) associated with
the process.
S (l) The state of the process.
UID (f,l) The user ID number of the process owner;
the login name is printed under the -f
option.
PID (all) The process ID of the process; it is
possible to kill a process if this datum is
known.
PPID (f,l) The process ID of the parent process.
C (f,l) Processor utilization for scheduling.
PRI (l) The priority of the process; higher numbers
mean lower priority.
NI (l) Nice value; used in priority computation.
ADDR (l) The address of the process.
SZ (l) The size in blocks of the core image of the
process.
WCHAN (l) The event for which the process is waiting
or sleeping; if blank, the process is
running.
STIME (f) Starting time of the process.
TTY (all) The controlling terminal for the process.
TIME (all) The cumulative execution time for the
process.
CMD (all) 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, ps 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 option -f, is written in square brackets.
The -o option allows the output format to be specified under user
control.
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 user=, 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:
ruser 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 representation otherwise.
user 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.
rgroup 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 representation otherwise.
group 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.
pid The decimal value of the process ID.
ppid The decimal value of the parent process ID.
pgid The decimal value of the process group ID.
pcpu 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 unspecified manner.
vsz The size of the process in (virtual) memory in 1024 byte
units as a decimal integer.
nice The decimal value of the nice value of the process; see
nice.
etime In the POSIX locale, the elapsed time since the process
was started, in the form:
[[dd-]hh:]mm:ss
where dd shall represent the number of days, hh the number
of hours, mm the number of minutes, and ss the number of
seconds. The dd field shall be a decimal integer. The hh,
mm, and ss fields shall be two-digit decimal integers
padded on the left with zeros.
time In the POSIX locale, the cumulative CPU time of the
process in the form:
[dd-]hh:mm:ss
The dd, hh, mm, and ss fields shall be as described in the
etime specifier.
tty The name of the controlling terminal of the process (if
any) in the same format used by the who utility.
comm The name of the command being executed (argv[0] value) as
a string.
args 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 <hyphen-minus> ('-') should be output in place of the field
value.
Only comm and args 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.
Table: Variable Names and Default Headers in ps
┌───────────────────────────────────┬───────────────────────────────────┐
│ Format Specifier Default Header │ Format Specifier Default Header │
├───────────────────────────────────┼───────────────────────────────────┤
│ args COMMAND │ ppid PPID │
│ comm COMMAND │ rgroup RGROUP │
│ etime ELAPSED │ ruser RUSER │
│ group GROUP │ time TIME │
│ nice NI │ tty TT │
│ pcpu %CPU │ user USER │
│ pgid PGID │ vsz VSZ │
│ pid PID │ │
└───────────────────────────────────┴───────────────────────────────────┘
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Default.
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.
The args 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 -o options can be used, such as:
ps -o "user=User Name" -o pid=Process\ ID
On some implementations, especially multi-level secure systems, ps
may be severely restricted and produce information only about
child processes owned by the user.
The command:
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 ps. 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 systems, ps 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.1‐2017 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 precluded this.
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.
The -A option is equivalent to the BSD -g and the SVID -e.
Because the two systems differed, a mnemonic compromise was
selected.
The -a 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.1‐2017 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 -o. 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 ps, talk, who, and write require that they all use
the same format.
The pcpu 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.
None.
kill(1p), nice(1p), renice(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. 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.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 PS(1P)
Pages that refer to this page: kill(1p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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