<s>
chsh	B-Device
(	O
an	O
abbreviation	O
of	O
"	O
change	O
shell	B-Application
"	O
)	O
is	O
a	O
command	B-Application
on	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
that	O
is	O
used	O
to	O
change	O
a	O
login	O
shell	B-Application
.	O
</s>
<s>
Users	O
can	O
either	O
supply	O
the	O
pathname	B-Application
of	O
the	O
shell	B-Application
that	O
they	O
wish	O
to	O
change	O
to	O
on	O
the	O
command	B-Application
line	O
,	O
or	O
supply	O
no	O
arguments	O
,	O
in	O
which	O
case	O
allows	O
the	O
user	O
to	O
change	O
the	O
shell	B-Application
interactively	O
.	O
</s>
<s>
The	O
superuser	B-Application
can	O
modify	O
the	O
shells	O
of	O
other	O
users	O
,	O
by	O
supplying	O
the	O
name	O
of	O
the	O
user	O
whose	O
shell	B-Application
is	O
to	O
be	O
modified	O
as	O
a	O
command-line	O
argument	O
.	O
</s>
<s>
For	O
security	O
reasons	O
,	O
the	O
shells	O
that	O
both	O
ordinary	O
users	O
and	O
the	O
superuser	B-Application
can	O
specify	O
are	O
limited	O
by	O
the	O
contents	O
of	O
the	O
file	O
,	O
with	O
the	O
pathname	B-Application
of	O
the	O
shell	B-Application
being	O
required	O
to	O
be	O
exactly	O
as	O
it	O
appears	O
in	O
that	O
file	O
.	O
</s>
<s>
(	O
This	O
security	O
feature	O
is	O
alterable	O
by	O
re-compiling	O
the	O
source	O
code	O
for	O
the	O
command	B-Application
with	O
a	O
different	O
configuration	O
option	O
,	O
and	O
thus	O
is	O
not	O
necessarily	O
enabled	O
on	O
all	O
systems	O
.	O
)	O
</s>
<s>
The	O
superuser	B-Application
can	O
,	O
however	O
,	O
also	O
modify	O
the	O
password	O
file	O
directly	O
,	O
setting	O
any	O
user	O
's	O
shell	B-Application
to	O
any	O
executable	O
file	O
on	O
the	O
system	O
without	O
reference	O
to	O
and	O
without	O
using	O
.	O
</s>
<s>
On	O
most	O
systems	O
,	O
when	O
is	O
invoked	O
without	O
the	O
command-line	O
option	O
(	O
to	O
specify	O
the	O
name	O
of	O
the	O
shell	B-Application
)	O
,	O
it	O
prompts	O
the	O
user	O
to	O
select	O
one	O
.	O
</s>
<s>
On	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
,	O
if	O
invoked	O
without	O
the	O
option	O
,	O
displays	O
a	O
text	O
file	O
in	O
the	O
default	O
editor	O
(	O
initially	O
set	O
to	O
vim	O
)	O
allowing	O
the	O
user	O
to	O
change	O
all	O
of	O
the	O
features	O
of	O
their	O
user	O
account	O
that	O
they	O
are	O
permitted	O
to	O
change	O
,	O
the	O
pathname	B-Application
of	O
the	O
shell	B-Application
being	O
the	O
name	O
next	O
to	O
"	O
Shell	B-Application
:	O
"	O
.	O
</s>
<s>
When	O
the	O
user	O
quits	O
vim	O
,	O
the	O
changes	O
made	O
there	O
are	O
transferred	O
to	O
the	O
/etc/passwd	O
file	O
which	O
only	O
root	O
can	O
change	O
directly	O
.	O
</s>
<s>
Depending	O
on	O
the	O
system	O
,	O
may	O
or	O
may	O
not	O
prompt	O
the	O
user	O
for	O
a	O
password	O
before	O
changing	O
the	O
shell	B-Application
,	O
or	O
entering	O
interactive	O
mode	O
.	O
</s>
<s>
On	O
many	O
Linux	B-Application
distributions	I-Application
,	O
the	O
command	B-Application
is	O
a	O
PAM-aware	O
application	O
.	O
</s>
<s>
As	O
such	O
,	O
its	O
behaviour	O
can	O
be	O
tailored	O
,	O
using	O
PAM	B-Application
configuration	O
options	O
,	O
for	O
individual	O
users	O
.	O
</s>
<s>
Most	O
Unix-like	B-Operating_System
systems	I-Operating_System
provide	O
.	O
</s>
<s>
SVr4-based	O
systems	O
provided	O
a	O
similar	O
capability	O
with	O
passwd	B-Protocol
.	O
</s>
<s>
Two	O
of	O
the	O
three	O
remaining	O
systems	O
(	O
IBM	B-Application
AIX	I-Application
and	O
HP-UX	B-Application
)	O
provide	O
in	O
addition	O
to	O
.	O
</s>
<s>
The	O
exception	O
is	O
Solaris	B-Application
,	O
where	O
non-administrators	O
are	O
unable	O
to	O
change	O
their	O
shell	B-Application
unless	O
a	O
network	O
name	O
server	O
such	O
as	O
NIS	B-Operating_System
or	O
NIS+	O
is	O
installed	O
.	O
</s>
<s>
The	O
obsolete	O
SGI	O
SVr4	O
system	O
IRIX64	B-Operating_System
also	O
lacked	O
.	O
</s>
