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<title>6.1.1 Process Parameters
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<H2><A NAME=
"SECTION008110000000000000000"></A><A NAME=
"os-procinfo"></A>
These functions and data items provide information and operate on the
current process and user.
<dl><dt><b><tt id='l2h-
1508' xml:id='l2h-
1508'
>environ
</tt></b></dt>
A mapping object representing the string environment. For example,
<code>environ['HOME']
</code> is the pathname of your home directory (on some
platforms), and is equivalent to
<code>getenv(
"HOME")
</code> in C.
This mapping is captured the first time the
<tt class=
"module">os
</tt> module is
imported, typically during Python startup as part of processing
<span class=
"file">site.py
</span>. Changes to the environment made after this time are
not reflected in
<code>os.environ
</code>, except for changes made by modifying
<code>os.environ
</code> directly.
If the platform supports the
<tt class=
"function">putenv()
</tt> function, this
mapping may be used to modify the environment as well as query the
environment.
<tt class=
"function">putenv()
</tt> will be called automatically when
<span class=
"note"><b class=
"label">Note:
</b>
Calling
<tt class=
"function">putenv()
</tt> directly does not change
<code>os.environ
</code>, so it's better to modify
<code>os.environ
</code>.
</span>
<span class=
"note"><b class=
"label">Note:
</b>
On some platforms, including FreeBSD and Mac OS X, setting
<code>environ
</code> may cause memory leaks. Refer to the system documentation
for
<tt class=
"cfunction">putenv()
</tt>.
</span>If
<tt class=
"function">putenv()
</tt> is not provided, a modified copy of this mapping
may be passed to the appropriate process-creation functions to cause
child processes to use a modified environment.
If the platform supports the
<tt class=
"function">unsetenv()
</tt> function, you can
delete items in this mapping to unset environment variables.
<tt class=
"function">unsetenv()
</tt> will be called automatically when an item is
deleted from
<code>os.environ
</code>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt class=
"function">chdir
</tt></b>(
</nobr></td>
<td><var>path
</var>)
</td></tr></table></dt>
<dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt class=
"function">fchdir
</tt></b>(
</nobr></td>
<td><var>fd
</var>)
</td></tr></table></dt>
<dd><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt class=
"function">getcwd
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
<dd>These functions are described in ``Files and Directories'' (section
<A href=
"os-file-dir.html#os-file-dir">6.1.4</A>).
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1509' xml:id='l2h-
1509'
class=
"function">ctermid
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
Return the filename corresponding to the controlling terminal of the
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1510' xml:id='l2h-
1510'
class=
"function">getegid
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
Return the effective group id of the current process. This
corresponds to the `set id' bit on the file being executed in the
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1511' xml:id='l2h-
1511'
class=
"function">geteuid
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
<a id='l2h-
1541' xml:id='l2h-
1541'
></a>
Return the current process' effective user id.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1512' xml:id='l2h-
1512'
class=
"function">getgid
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
<a id='l2h-
1542' xml:id='l2h-
1542'
></a>
Return the real group id of the current process.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1513' xml:id='l2h-
1513'
class=
"function">getgroups
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
Return list of supplemental group ids associated with the current
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1514' xml:id='l2h-
1514'
class=
"function">getlogin
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
Return the name of the user logged in on the controlling terminal of
the process. For most purposes, it is more useful to use the
environment variable
<a class=
"envvar" id='l2h-
1543' xml:id='l2h-
1543'
>LOGNAME
</a> to find out who the user is,
or
<code>pwd.getpwuid(os.getuid())[
0]
</code> to get the login name
of the currently effective user ID.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1515' xml:id='l2h-
1515'
class=
"function">getpgid
</tt></b>(
</nobr></td>
<td><var>pid
</var>)
</td></tr></table></dt>
Return the process group id of the process with process id
<var>pid
</var>.
If
<var>pid
</var> is
0, the process group id of the current process is
returned. Availability:
<span class=
"Unix">Unix
</span>.
<span class=
"versionnote">New in version
2.3.
</span>
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1516' xml:id='l2h-
1516'
class=
"function">getpgrp
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
<a id='l2h-
1544' xml:id='l2h-
1544'
></a>
Return the id of the current process group.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1517' xml:id='l2h-
1517'
class=
"function">getpid
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
<a id='l2h-
1545' xml:id='l2h-
1545'
></a>
Return the current process id.
Availability:
<span class=
"Unix">Unix
</span>, Windows.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1518' xml:id='l2h-
1518'
class=
"function">getppid
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
<a id='l2h-
1546' xml:id='l2h-
1546'
></a>
Return the parent's process id.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1519' xml:id='l2h-
1519'
class=
"function">getuid
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
<a id='l2h-
1547' xml:id='l2h-
1547'
></a>
Return the current process' user id.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1520' xml:id='l2h-
1520'
class=
"function">getenv
</tt></b>(
</nobr></td>
<td><var>varname
</var><big>[
</big><var>, value
</var><big>]
</big><var></var>)
</td></tr></table></dt>
Return the value of the environment variable
<var>varname
</var> if it
exists, or
<var>value
</var> if it doesn't.
<var>value
</var> defaults to
Availability: most flavors of
<span class=
"Unix">Unix
</span>, Windows.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1521' xml:id='l2h-
1521'
class=
"function">putenv
</tt></b>(
</nobr></td>
<td><var>varname, value
</var>)
</td></tr></table></dt>
<a id='l2h-
1548' xml:id='l2h-
1548'
></a>
Set the environment variable named
<var>varname
</var> to the string
<var>value
</var>. Such changes to the environment affect subprocesses
started with
<tt class=
"function">os.system()
</tt>,
<tt class=
"function">popen()
</tt> or
<tt class=
"function">fork()
</tt> and
<tt class=
"function">execv()
</tt>.
Availability: most flavors of
<span class=
"Unix">Unix
</span>, Windows.
<span class=
"note"><b class=
"label">Note:
</b>
On some platforms, including FreeBSD and Mac OS X,
setting
<code>environ
</code> may cause memory leaks.
Refer to the system documentation for putenv.
</span>When
<tt class=
"function">putenv()
</tt> is
supported, assignments to items in
<code>os.environ
</code> are automatically
translated into corresponding calls to
<tt class=
"function">putenv()
</tt>; however,
calls to
<tt class=
"function">putenv()
</tt> don't update
<code>os.environ
</code>, so it is
actually preferable to assign to items of
<code>os.environ
</code>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1522' xml:id='l2h-
1522'
class=
"function">setegid
</tt></b>(
</nobr></td>
<td><var>egid
</var>)
</td></tr></table></dt>
Set the current process's effective group id.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1523' xml:id='l2h-
1523'
class=
"function">seteuid
</tt></b>(
</nobr></td>
<td><var>euid
</var>)
</td></tr></table></dt>
Set the current process's effective user id.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1524' xml:id='l2h-
1524'
class=
"function">setgid
</tt></b>(
</nobr></td>
<td><var>gid
</var>)
</td></tr></table></dt>
Set the current process' group id.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1525' xml:id='l2h-
1525'
class=
"function">setgroups
</tt></b>(
</nobr></td>
<td><var>groups
</var>)
</td></tr></table></dt>
Set the list of supplemental group ids associated with the current
process to
<var>groups
</var>.
<var>groups
</var> must be a sequence, and each
element must be an integer identifying a group. This operation is
typical available only to the superuser.
Availability:
<span class=
"Unix">Unix
</span>.
<span class=
"versionnote">New in version
2.2.
</span>
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1526' xml:id='l2h-
1526'
class=
"function">setpgrp
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
Calls the system call
<tt class=
"cfunction">setpgrp()
</tt> or
<tt class=
"cfunction">setpgrp(
0,
0)
</tt> depending on which version is implemented (if any). See the
<span class=
"Unix">Unix
</span> manual for the semantics.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1527' xml:id='l2h-
1527'
class=
"function">setpgid
</tt></b>(
</nobr></td>
<td><var>pid, pgrp
</var>)
</td></tr></table></dt>
<dd> Calls the system call
<tt class=
"cfunction">setpgid()
</tt> to set the process group id of the process with
id
<var>pid
</var> to the process group with id
<var>pgrp
</var>. See the
<span class=
"Unix">Unix
</span>manual for the semantics.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1528' xml:id='l2h-
1528'
class=
"function">setreuid
</tt></b>(
</nobr></td>
<td><var>ruid, euid
</var>)
</td></tr></table></dt>
Set the current process's real and effective user ids.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1529' xml:id='l2h-
1529'
class=
"function">setregid
</tt></b>(
</nobr></td>
<td><var>rgid, egid
</var>)
</td></tr></table></dt>
Set the current process's real and effective group ids.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1530' xml:id='l2h-
1530'
class=
"function">getsid
</tt></b>(
</nobr></td>
<td><var>pid
</var>)
</td></tr></table></dt>
Calls the system call
<tt class=
"cfunction">getsid()
</tt>. See the
<span class=
"Unix">Unix
</span> manual
Availability:
<span class=
"Unix">Unix
</span>.
<span class=
"versionnote">New in version
2.4.
</span>
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1531' xml:id='l2h-
1531'
class=
"function">setsid
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
Calls the system call
<tt class=
"cfunction">setsid()
</tt>. See the
<span class=
"Unix">Unix
</span> manual
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1532' xml:id='l2h-
1532'
class=
"function">setuid
</tt></b>(
</nobr></td>
<td><var>uid
</var>)
</td></tr></table></dt>
<a id='l2h-
1549' xml:id='l2h-
1549'
></a>
Set the current process' user id.
Availability:
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1533' xml:id='l2h-
1533'
class=
"function">strerror
</tt></b>(
</nobr></td>
<td><var>code
</var>)
</td></tr></table></dt>
Return the error message corresponding to the error code in
Availability:
<span class=
"Unix">Unix
</span>, Windows.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1534' xml:id='l2h-
1534'
class=
"function">umask
</tt></b>(
</nobr></td>
<td><var>mask
</var>)
</td></tr></table></dt>
Set the current numeric umask and returns the previous umask.
Availability:
<span class=
"Unix">Unix
</span>, Windows.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1535' xml:id='l2h-
1535'
class=
"function">uname
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
Return a
5-tuple containing information identifying the current
operating system. The tuple contains
5 strings:
<code>(
<var>sysname
</var>,
<var>nodename
</var>,
<var>release
</var>,
<var>version
</var>,
<var>machine
</var>)
</code>. Some systems truncate the nodename to
8
characters or to the leading component; a better way to get the
hostname is
<tt class=
"function">socket.gethostname()
</tt><a id='l2h-
1537' xml:id='l2h-
1537'
></a>or even
<a id='l2h-
1539' xml:id='l2h-
1539'
></a><code>socket.gethostbyaddr(socket.gethostname())
</code>.
Availability: recent flavors of
<span class=
"Unix">Unix
</span>.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
1540' xml:id='l2h-
1540'
class=
"function">unsetenv
</tt></b>(
</nobr></td>
<td><var>varname
</var>)
</td></tr></table></dt>
<a id='l2h-
1550' xml:id='l2h-
1550'
></a>
Unset (delete) the environment variable named
<var>varname
</var>. Such
changes to the environment affect subprocesses started with
<tt class=
"function">os.system()
</tt>,
<tt class=
"function">popen()
</tt> or
<tt class=
"function">fork()
</tt> and
<tt class=
"function">execv()
</tt>. Availability: most flavors of
<span class=
"Unix">Unix
</span>, Windows.
When
<tt class=
"function">unsetenv()
</tt> is
supported, deletion of items in
<code>os.environ
</code> is automatically
translated into a corresponding call to
<tt class=
"function">unsetenv()
</tt>; however,
calls to
<tt class=
"function">unsetenv()
</tt> don't update
<code>os.environ
</code>, so it is
actually preferable to delete items of
<code>os.environ
</code>.
<div class='online-navigation'
>
<table align=
"center" width=
"100%" cellpadding=
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