The fact that system
ignores interrupts is often
not what a program wants. ISO POSIX (2003)
describes some of the consequences; an
additional consequence is that a program calling system
from a loop cannot be reliably interrupted. Many programs will want to use
the exec
family of functions instead.
Do not use system
from a program with
suid or sgid privileges,
because unexpected values for some environment variables might be used
to subvert system integrity. Use the exec
family of functions instead, but not execlp
or execvp
. system
will
not, in fact, work properly from programs with suid
or sgid privileges on systems on which
/bin/sh is bash version 2,
since bash 2 drops privileges on startup.
(Debian uses a modified bash which does not do
this when invoked as sh.)
The check for the availability of /bin/sh is not actually performed; it is always assumed to be available. ISO C (1999) specifies the check, but ISO POSIX (2003) specifies that the return shall always be nonzero, since a system without the shell is not conforming, and it is this that is implemented.
It is possible for the shell command to return
127, so that code is not a sure
indication that the execve
call failed; check
the global variable errno to make sure.