вызвать утилиту с измененным значением nice (invoke a utility with an altered nice value)
Пролог (Prolog)
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.
Имя (Name)
nice — invoke a utility with an altered nice value
Синопсис (Synopsis)
nice [-n increment] utility [argument...]
Описание (Description)
The nice utility shall invoke a utility, requesting that it be
run with a different nice value (see the Base Definitions volume
of POSIX.1‐2017, Section 3.244, Nice Value). With no options,
the executed utility shall be run with a nice value that is some
implementation-defined quantity greater than or equal to the nice
value of the current process. If the user lacks appropriate
privileges to affect the nice value in the requested manner, the
nice utility shall not affect the nice value; in this case, a
warning message may be written to standard error, but this shall
not prevent the invocation of utility or affect the exit status.
Параметры (Options)
The nice utility shall conform to the Base Definitions volume of
POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
The following option is supported:
-n increment
A positive or negative decimal integer which shall have
the same effect on the execution of the utility as if
the utility had called the nice() function with the
numeric value of the increment option-argument.
Операнды (Operands)
The following operands shall be supported:
utility The name of a utility that is to be invoked. If the
utility operand names any of the special built-in
utilities in Section 2.14, Special Built-In Utilities,
the results are undefined.
argument Any string to be supplied as an argument when invoking
the utility named by the utility operand.
Стандартный ввод (Stdin)
Not used.
Входные файлы (Input files)
None.
Переменные окружения (Environment variables)
The following environment variables shall affect the execution of
nice:
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 for 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.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
PATH Determine the search path used to locate the utility to
be invoked. See the Base Definitions volume of
POSIX.1‐2017, Chapter 8, Environment Variables.
Асинхронные события (Asynchronous events)
Default.
Стандартный вывод (Stdout)
Not used.
Стандартный вывод сообщений (Stderr)
The standard error shall be used only for diagnostic messages.
Выходные файлы (Output files)
None.
Расширенное описание (Extended description)
None.
Статус выхода (Exit)
If utility is invoked, the exit status of nice shall be the exit
status of utility; otherwise, the nice utility shall exit with
one of the following values:
1‐125 An error occurred in the nice utility.
126 The utility specified by utility was found but could not
be invoked.
127 The utility specified by utility could not be found.
Последствия ошибок (Consequences of errors)
Default.
The following sections are informative.
Использование в приложениях (Application usage)
The only guaranteed portable uses of this utility are:
nice utility
Run utility with the default higher or equal nice value.
nice -n <positive integer> utility
Run utility with a higher nice value.
On some implementations they have no discernible effect on the
invoked utility and on some others they are exactly equivalent.
Historical systems have frequently supported the <positive
integer> up to 20. Since there is no error penalty associated
with guessing a number that is too high, users without access to
the system conformance document (to see what limits are actually
in place) could use the historical 1 to 20 range or attempt to
use very large numbers if the job should be truly low priority.
The nice value of a process can be displayed using the command:
ps -o nice
The command, env, nice, nohup, time, and xargs utilities have
been specified to use exit code 127 if an error occurs so that
applications can distinguish ``failure to find a utility'' from
``invoked utility exited with an error indication''. The value
127 was chosen because it is not commonly used for other
meanings; most utilities use small values for ``normal error
conditions'' and the values above 128 can be confused with
termination due to receipt of a signal. The value 126 was chosen
in a similar manner to indicate that the utility could be found,
but not invoked. Some scripts produce meaningful error messages
differentiating the 126 and 127 cases. The distinction between
exit codes 126 and 127 is based on KornShell practice that uses
127 when all attempts to exec the utility fail with [ENOENT], and
uses 126 when any attempt to exec the utility fails for any other
reason.
Примеры (Examples)
None.
Обоснование (Rationale)
The 4.3 BSD version of nice does not check whether increment is a
valid decimal integer. The command nice -x utility, for example,
would be treated the same as the command nice --1 utility. If
the user does not have appropriate privileges, this results in a
``permission denied'' error. This is considered a bug.
When a user without appropriate privileges gives a negative
increment, System V treats it like the command nice -0 utility,
while 4.3 BSD writes a ``permission denied'' message and does not
run the utility. The standard specifies the System V behavior
together with an optional BSD-style ``permission denied''
message.
The C shell has a built-in version of nice that has a different
interface from the one described in this volume of POSIX.1‐2017.
The term ``utility'' is used, rather than ``command'', to
highlight the fact that shell compound commands, pipelines, and
so on, cannot be used. Special built-ins also cannot be used.
However, ``utility'' includes user application programs and shell
scripts, not just utilities defined in this volume of
POSIX.1‐2017.
Historical implementations of nice provide a nice value range of
40 or 41 discrete steps, with the default nice value being the
midpoint of that range. By default, they raise the nice value of
the executed utility by 10.
Some historical documentation states that the increment value
must be within a fixed range. This is misleading; the valid
increment values on any invocation are determined by the current
process nice value, which is not always the default.
The definition of nice value is not intended to suggest that all
processes in a system have priorities that are comparable.
Scheduling policy extensions such as the realtime priorities in
the System Interfaces volume of POSIX.1‐2017 make the notion of a
single underlying priority for all scheduling policies
problematic. Some implementations may implement the nice-related
features to affect all processes on the system, others to affect
just the general time-sharing activities implied by this volume
of POSIX.1‐2017, and others may have no effect at all. Because of
the use of ``implementation-defined'' in nice and renice, a wide
range of implementation strategies are possible.
Earlier versions of this standard allowed a -increment option.
This form is no longer specified by POSIX.1‐2008 but may be
present in some implementations.
Будущие направления (Future directions)
None.
Смотри также (See also)
Chapter 2, Shell Command Language, renice(1p)
The Base Definitions volume of POSIX.1‐2017, Section 3.244, Nice
Value, Chapter 8, Environment Variables, Section 12.2, Utility
Syntax Guidelines
The System Interfaces volume of POSIX.1‐2017, nice(3p)
