<s>
The	O
restricted	B-Operating_System
shell	I-Operating_System
is	O
a	O
Unix	B-Application
shell	I-Application
that	O
restricts	O
some	O
of	O
the	O
capabilities	O
available	O
to	O
an	O
interactive	O
user	O
session	O
,	O
or	O
to	O
a	O
shell	B-Language
script	I-Language
,	O
running	O
within	O
it	O
.	O
</s>
<s>
A	O
restricted	O
mode	O
operation	O
is	O
found	O
in	O
the	O
original	O
Bourne	B-Device
shell	I-Device
and	O
its	O
later	O
counterpart	O
,	O
and	O
in	O
the	O
KornShell	B-Language
.	O
</s>
<s>
In	O
some	O
cases	O
a	O
restricted	B-Operating_System
shell	I-Operating_System
is	O
used	O
in	O
conjunction	O
with	O
a	O
chroot	B-Application
jail	I-Application
,	O
in	O
a	O
further	O
attempt	O
to	O
limit	O
access	O
to	O
the	O
system	O
as	O
a	O
whole	O
.	O
</s>
<s>
The	O
restricted	O
mode	O
of	O
the	B-Device
Bourne	I-Device
shell	I-Device
,	O
and	O
its	O
POSIX	O
workalikes	O
,	O
is	O
used	O
when	O
the	O
interpreter	O
is	O
invoked	O
in	O
one	O
of	O
the	O
following	O
ways	O
:	O
</s>
<s>
The	O
restricted	O
mode	O
of	O
Bash	B-Operating_System
is	O
used	O
when	O
Bash	B-Operating_System
is	O
invoked	O
in	O
one	O
of	O
the	O
following	O
ways	O
:	O
</s>
<s>
Similarly	O
KornShell	B-Language
's	O
restricted	O
mode	O
is	O
produced	O
by	O
invoking	O
it	O
thus	O
:	O
</s>
<s>
Though	O
this	O
invokes	O
Bash	B-Operating_System
directly	O
,	O
without	O
the	O
or	O
options	O
,	O
Bash	B-Operating_System
does	O
recognize	O
that	O
it	O
was	O
invoked	O
through	O
and	O
it	O
does	O
come	O
up	O
as	O
a	O
restricted	B-Operating_System
shell	I-Operating_System
.	O
</s>
<s>
This	O
can	O
be	O
accomplished	O
with	O
the	O
following	O
simple	O
commands	O
(	O
executed	O
as	O
root	O
,	O
either	O
logged	O
in	O
as	O
user	O
root	O
,	O
or	O
using	O
sudo	B-Device
)	O
:	O
</s>
<s>
The	O
following	O
operations	O
are	O
not	O
permitted	O
in	O
a	O
restricted	B-Operating_System
shell	I-Operating_System
:	O
</s>
<s>
Bash	B-Operating_System
adds	O
further	O
restrictions	O
,	O
including	O
:	O
</s>
<s>
Restrictions	O
in	O
the	O
restricted	O
KornShell	B-Language
are	O
much	O
the	O
same	O
as	O
those	O
in	O
the	O
restricted	O
Bourne	B-Device
shell	I-Device
.	O
</s>
<s>
The	O
restricted	B-Operating_System
shell	I-Operating_System
is	O
not	O
secure	O
.	O
</s>
<s>
The	O
following	O
is	O
an	O
example	O
of	O
the	O
shell	O
function	O
in	O
vi	B-Application
being	O
used	O
to	O
escape	O
from	O
the	O
restricted	B-Operating_System
shell	I-Operating_System
:	O
</s>
<s>
Beyond	O
the	O
restricted	O
modes	O
of	O
usual	O
shells	O
,	O
specialized	O
restricted	B-Operating_System
shell	I-Operating_System
programs	O
include	O
:	O
</s>
