1RCMD(3) Linux Programmer's Manual RCMD(3)
2
6 rcmd, rresvport, iruserok, ruserok - routines for returning a stream to
7 a remote command
8
10 #include <netdb.h> /* Or <unistd.h> on some systems */
11 int rcmd(char **ahost, int inport, const char *locuser,
13 const char *remuser, const char *cmd, int *fd2p);
14 int rresvport(int *port);
16 int iruserok(uint32_t raddr, int superuser,
18 const char *ruser, const char *luser);
19 int ruserok(const char *rhost, int superuser,
21 const char *ruser, const char *luser);
22 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
24 rcmd(), rresvport(), ruserok(): _BSD_SOURCE
26
28 The rcmd() function is used by the superuser to execute a command on a
29 remote machine using an authentication scheme based on privileged port
30 numbers. The rresvport() function returns a descriptor to a socket
31 with an address in the privileged port space. The iruserok() and
32 ruserok() functions are used by servers to authenticate clients
33 requesting service with rcmd(). All four functions are present in the
34 same file and are used by the rshd(8) server (among others).
35 The rcmd() function looks up the host *ahost using gethostbyname(3),
37 returning -1 if the host does not exist. Otherwise *ahost is set to
38 the standard name of the host and a connection is established to a
39 server residing at the well-known Internet port inport.
40 If the connection succeeds, a socket in the Internet domain of type
42 SOCK_STREAM is returned to the caller, and given to the remote command
43 as stdin and stdout. If fd2p is nonzero, then an auxiliary channel to
44 a control process will be set up, and a descriptor for it will be
45 placed in *fd2p. The control process will return diagnostic output
46 from the command (unit 2) on this channel, and will also accept bytes
47 on this channel as being Unix signal numbers, to be forwarded to the
48 process group of the command. If fd2p is 0, then the stderr (unit 2 of
49 the remote command) will be made the same as the stdout and no provi‐
50 sion is made for sending arbitrary signals to the remote process,
51 although you may be able to get its attention by using out-of-band
52 data.
53 The protocol is described in detail in rshd(8).
55 The rresvport() function is used to obtain a socket with a privileged
57 address bound to it. This socket is suitable for use by rcmd() and
58 several other functions. Privileged Internet ports are those in the
59 range 0 to 1023. Only the superuser is allowed to bind an address of
60 this sort to a socket.
61 The iruserok() and ruserok() functions take a remote host's IP address
63 or name, respectively, two usernames and a flag indicating whether the
64 local user's name is that of the superuser. Then, if the user is not
65 the superuser, it checks the /etc/hosts.equiv file. If that lookup is
66 not done, or is unsuccessful, the .rhosts in the local user's home
67 directory is checked to see if the request for service is allowed.
68 If this file does not exist, is not a regular file, is owned by anyone
70 other than the user or the superuser, or is writable by anyone other
71 than the owner, the check automatically fails. Zero is returned if the
72 machine name is listed in the hosts.equiv file, or the host and remote
73 username are found in the .rhosts file; otherwise iruserok() and
74 ruserok() return -1. If the local domain (as obtained from gethost‐
75 name(2)) is the same as the remote domain, only the machine name need
76 be specified.
77 If the IP address of the remote host is known, iruserok() should be
79 used in preference to ruserok(), as it does not require trusting the
80 DNS server for the remote host's domain.
81
83 The rcmd() function returns a valid socket descriptor on success. It
84 returns -1 on error and prints a diagnostic message on the standard
85 error.
86 The rresvport() function returns a valid, bound socket descriptor on
88 success. It returns -1 on error with the global value errno set
89 according to the reason for failure. The error code EAGAIN is over‐
90 loaded to mean "All network ports in use."
91
93 Not in POSIX.1-2001. Present on the BSDs, Solaris, and many other sys‐
94 tems. These functions appeared in 4.2BSD.
95
97 iruserok() is not declared in glibc headers.
98
100 rlogin(1), rsh(1), intro(2), rexec(3), rexecd(8), rlogind(8), rshd(8)
101
103 This page is part of release 3.25 of the Linux man-pages project. A
104 description of the project, and information about reporting bugs, can
105 be found at http://www.kernel.org/doc/man-pages/.
106Linux 2007-12-28 RCMD(3)