NAME | SYNOPSIS | DESCRIPTION | CONFORMING TO | VERSIONS | EXAMPLE | SEE ALSO | COLOPHON

SOCK_DIAG(7)              Linux Programmer's Manual             SOCK_DIAG(7)

NAME         top

       sock_diag - obtaining information about sockets

SYNOPSIS         top

       #include <sys/socket.h>
       #include <linux/sock_diag.h>
       #include <linux/unix_diag.h> /* for UNIX domain sockets */
       #include <linux/inet_diag.h> /* for IPv4 and IPv6 sockets */

       diag_socket = socket(AF_NETLINK, socket_type, NETLINK_SOCK_DIAG);

DESCRIPTION         top

       The sock_diag netlink subsystem provides a mechanism for obtaining
       information about sockets of various address families from the
       kernel.  This subsystem can be used to obtain information about
       individual sockets or request a list of sockets.

       In the request, the caller can specify additional information it
       would like to obtain about the socket, for example, memory
       information or information specific to the address family.

       When requesting a list of sockets, the caller can specify filters
       that would be applied by the kernel to select a subset of sockets to
       report.  For now, there is only the ability to filter sockets by
       state (connected, listening, and so on.)

       Note that sock_diag reports only those sockets that have a name; that
       is, either sockets bound explicitly with bind(2) or sockets that were
       automatically bound to an address (e.g., by connect(2)).  This is the
       same set of sockets that is available via /proc/net/unix,
       /proc/net/tcp, /proc/net/udp, and so on.

   Request
       The request starts with a struct nlmsghdr header described in
       netlink(7) with nlmsg_type field set to SOCK_DIAG_BY_FAMILY.  It is
       followed by a header specific to the address family that starts with
       a common part shared by all address families:

           struct sock_diag_req {
               __u8 sdiag_family;
               __u8 sdiag_protocol;
           };

       The fields of this structure are as follows:

       sdiag_family
              An address family.  It should be set to the appropriate AF_*
              constant.

       sdiag_protocol
              Depends on sdiag_family.  It should be set to the appropriate
              IPPROTO_* constant for AF_INET and AF_INET6, and to 0
              otherwise.

       If the nlmsg_flags field of the struct nlmsghdr header has the
       NLM_F_DUMP flag set, it means that a list of sockets is being
       requested; otherwise it is a query about an individual socket.

   Response
       The response starts with a struct nlmsghdr header and is followed by
       an array of objects specific to the address family.  The array is to
       be accessed with the standard NLMSG_* macros from the netlink(3) API.

       Each object is the NLA (netlink attributes) list that is to be
       accessed with the RTA_* macros from rtnetlink(3) API.

   UNIX domain sockets
       For UNIX domain sockets the request is represented in the following
       structure:

           struct unix_diag_req {
               __u8    sdiag_family;
               __u8    sdiag_protocol;
               __u16   pad;
               __u32   udiag_states;
               __u32   udiag_ino;
               __u32   udiag_show;
               __u32   udiag_cookie[2];
           };

       The fields of this structure are as follows:

       sdiag_family
              The address family; it should be set to AF_UNIX.

       sdiag_protocol
       pad    These fields should be set to 0.

       udiag_states
              This is a bit mask that defines a filter of sockets states.
              Only those sockets whose states are in this mask will be
              reported.  Ignored when querying for an individual socket.
              Supported values are:

                   1 << TCP_ESTABLISHED

                   1 << TCP_LISTEN

       udiag_ino
              This is an inode number when querying for an individual
              socket.  Ignored when querying for a list of sockets.

       udiag_show
              This is a set of flags defining what kind of information to
              report.  Each requested kind of information is reported back
              as a netlink attribute as described below:

              UDIAG_SHOW_NAME
                     The attribute reported in answer to this request is
                     UNIX_DIAG_NAME.  The payload associated with this
                     attribute is the pathname to which the socket was bound
                     (a sequence of bytes up to UNIX_PATH_MAX length).

              UDIAG_SHOW_VFS
                     The attribute reported in answer to this request is
                     UNIX_DIAG_VFS.  The payload associated with this
                     attribute is represented in the following structure:

                         struct unix_diag_vfs {
                             __u32 udiag_vfs_dev;
                             __u32 udiag_vfs_ino;
                         };

                     The fields of this structure are as follows:

                     udiag_vfs_dev
                            The device number of the corresponding on-disk
                            socket inode.

                     udiag_vfs_ino
                            The inode number of the corresponding on-disk
                            socket inode.

              UDIAG_SHOW_PEER
                     The attribute reported in answer to this request is
                     UNIX_DIAG_PEER.  The payload associated with this
                     attribute is a __u32 value which is the peer's inode
                     number.  This attribute is reported for connected
                     sockets only.

              UDIAG_SHOW_ICONS
                     The attribute reported in answer to this request is
                     UNIX_DIAG_ICONS.  The payload associated with this
                     attribute is an array of __u32 values which are inode
                     numbers of sockets that has passed the connect(2) call,
                     but hasn't been processed with accept(2) yet.  This
                     attribute is reported for listening sockets only.

              UDIAG_SHOW_RQLEN
                     The attribute reported in answer to this request is
                     UNIX_DIAG_RQLEN.  The payload associated with this
                     attribute is represented in the following structure:

                         struct unix_diag_rqlen {
                             __u32 udiag_rqueue;
                             __u32 udiag_wqueue;
                         };

                     The fields of this structure are as follows:

                     udiag_rqueue
                            For listening sockets: the number of pending
                            connections.  The length of the array associated
                            with the UNIX_DIAG_ICONS response attribute is
                            equal to this value.

                            For established sockets: the amount of data in
                            incoming queue.

                     udiag_wqueue
                            For listening sockets: the backlog length which
                            equals to the value passed as the second
                            argument to listen(2).

                            For established sockets: the amount of memory
                            available for sending.

              UDIAG_SHOW_MEMINFO
                     The attribute reported in answer to this request is
                     UNIX_DIAG_MEMINFO.  The payload associated with this
                     attribute is an array of __u32 values described below
                     in the subsection "Socket memory information".

              The following attributes are reported back without any
              specific request:

              UNIX_DIAG_SHUTDOWN
                     The payload associated with this attribute is __u8
                     value which represents bits of shutdown(2) state.

       udiag_cookie
              This is an array of opaque identifiers that could be used
              along with udiag_ino to specify an individual socket.  It is
              ignored when querying for a list of sockets, as well as when
              all its elements are set to -1.

       The response to a query for UNIX domain sockets is represented as an
       array of

           struct unix_diag_msg {
               __u8    udiag_family;
               __u8    udiag_type;
               __u8    udiag_state;
               __u8    pad;
               __u32   udiag_ino;
               __u32   udiag_cookie[2];
           };

       followed by netlink attributes.

       The fields of this structure are as follows:

       udiag_family
              This field has the same meaning as in struct unix_diag_req.

       udiag_type
              This is set to one of SOCK_PACKET, SOCK_STREAM, or
              SOCK_SEQPACKET.

       udiag_state
              This is set to one of TCP_LISTEN or TCP_ESTABLISHED.

       pad    This field is set to 0.

       udiag_ino
              This is the socket inode number.

       udiag_cookie
              This is an array of opaque identifiers that could be used in
              subsequent queries.

   IPv4 and IPv6 sockets
       For IPv4 and IPv6 sockets, the request is represented in the
       following structure:

           struct inet_diag_req_v2 {
               __u8    sdiag_family;
               __u8    sdiag_protocol;
               __u8    idiag_ext;
               __u8    pad;
               __u32   idiag_states;
               struct inet_diag_sockid id;
           };

       where struct inet_diag_sockid is defined as follows:

           struct inet_diag_sockid {
               __be16  idiag_sport;
               __be16  idiag_dport;
               __be32  idiag_src[4];
               __be32  idiag_dst[4];
               __u32   idiag_if;
               __u32   idiag_cookie[2];
           };

       The fields of struct inet_diag_req_v2 are as follows:

       sdiag_family
              This should be set to either AF_INET or AF_INET6 for IPv4 or
              IPv6 sockets respectively.

       sdiag_protocol
              This should be set to one of IPPROTO_TCP, IPPROTO_UDP, or
              IPPROTO_UDPLITE.

       idiag_ext
              This is a set of flags defining what kind of extended
              information to report.  Each requested kind of information is
              reported back as a netlink attribute as described below:

              INET_DIAG_TOS
                     The payload associated with this attribute is a __u8
                     value which is the TOS of the socket.

              INET_DIAG_TCLASS
                     The payload associated with this attribute is a __u8
                     value which is the TClass of the socket.  IPv6 sockets
                     only.  For LISTEN and CLOSE sockets, this is followed
                     by INET_DIAG_SKV6ONLY attribute with associated __u8
                     payload value meaning whether the socket is IPv6-only
                     or not.

              INET_DIAG_MEMINFO
                     The payload associated with this attribute is
                     represented in the following structure:

                         struct inet_diag_meminfo {
                             __u32 idiag_rmem;
                             __u32 idiag_wmem;
                             __u32 idiag_fmem;
                             __u32 idiag_tmem;
                         };

                     The fields of this structure are as follows:

                     idiag_rmem  The amount of data in the receive queue.

                     idiag_wmem  The amount of data that is queued by TCP
                                 but not yet sent.

                     idiag_fmem  The amount of memory scheduled for future
                                 use (TCP only).

                     idiag_tmem  The amount of data in send queue.

              INET_DIAG_SKMEMINFO
                     The payload associated with this attribute is an array
                     of __u32 values described below in the subsection
                     "Socket memory information".

              INET_DIAG_INFO
                     The payload associated with this attribute is specific
                     to the address family.  For TCP sockets, it is an
                     object of type struct tcp_info.

              INET_DIAG_CONG
                     The payload associated with this attribute is a string
                     that describes the congestion control algorithm used.
                     For TCP sockets only.

       pad    This should be set to 0.

       idiag_states
              This is a bit mask that defines a filter of socket states.
              Only those sockets whose states are in this mask will be
              reported.  Ignored when querying for an individual socket.

       id     This is a socket ID object that is used in dump requests, in
              queries about individual sockets, and is reported back in each
              response.  Unlike UNIX domain sockets, IPv4 and IPv6 sockets
              are identified using addresses and ports.  All values are in
              network byte order.

       The fields of struct inet_diag_sockid are as follows:

       idiag_sport
              The source port.

       idiag_dport
              The destination port.

       idiag_src
              The source address.

       idiag_dst
              The destination address.

       idiag_if
              The interface number the socket is bound to.

       idiag_cookie
              This is an array of opaque identifiers that could be used
              along with other fields of this structure to specify an
              individual socket.  It is ignored when querying for a list of
              sockets, as well as when all its elements are set to -1.

       The response to a query for IPv4 or IPv6 sockets is represented as an
       array of

           struct inet_diag_msg {
               __u8    idiag_family;
               __u8    idiag_state;
               __u8    idiag_timer;
               __u8    idiag_retrans;

               struct inet_diag_sockid id;

               __u32   idiag_expires;
               __u32   idiag_rqueue;
               __u32   idiag_wqueue;
               __u32   idiag_uid;
               __u32   idiag_inode;
           };

       followed by netlink attributes.

       The fields of this structure are as follows:

       idiag_family
              This is the same field as in struct inet_diag_req_v2.

       idiag_state
              This denotes socket state as in struct inet_diag_req_v2.

       idiag_timer
              For TCP sockets, this field describes the type of timer that
              is currently active for the socket.  It is set to one of the
              following constants:

                   0      no timer is active
                   1      a retransmit timer
                   2      a keep-alive timer
                   3      a TIME_WAIT timer
                   4      a zero window probe timer

              For non-TCP sockets, this field is set to 0.

       idiag_retrans
              For idiag_timer values 1, 2, and 4, this field contains the
              number of retransmits.  For other idiag_timer values, this
              field is set to 0.

       idiag_expires
              For TCP sockets that have an active timer, this field
              describes its expiration time in milliseconds.  For other
              sockets, this field is set to 0.

       idiag_rqueue
              For listening sockets: the number of pending connections.

              For other sockets: the amount of data in the incoming queue.

       idiag_wqueue
              For listening sockets: the backlog length.

              For other sockets: the amount of memory available for sending.

       idiag_uid
              This is the socket owner UID.

       idiag_inode
              This is the socket inode number.

   Socket memory information
       The payload associated with UNIX_DIAG_MEMINFO and INET_DIAG_SKMEMINFO
       netlink attributes is an array of the following __u32 values:

       SK_MEMINFO_RMEM_ALLOC
              The amount of data in receive queue.

       SK_MEMINFO_RCVBUF
              The receive socket buffer as set by SO_RCVBUF.

       SK_MEMINFO_WMEM_ALLOC
              The amount of data in send queue.

       SK_MEMINFO_SNDBUF
              The send socket buffer as set by SO_SNDBUF.

       SK_MEMINFO_FWD_ALLOC
              The amount of memory scheduled for future use (TCP only).

       SK_MEMINFO_WMEM_QUEUED
              The amount of data queued by TCP, but not yet sent.

       SK_MEMINFO_OPTMEM
              The amount of memory allocated for the socket's service needs
              (e.g., socket filter).

       SK_MEMINFO_BACKLOG
              The amount of packets in the backlog (not yet processed).

CONFORMING TO         top

       The NETLINK_SOCK_DIAG API is Linux-specific.

VERSIONS         top

       NETLINK_INET_DIAG was introduced in Linux 2.6.14 and supported
       AF_INET and AF_INET6 sockets only.  In Linux 3.3, it was renamed to
       NETLINK_SOCK_DIAG and extended to support AF_UNIX sockets.

       UNIX_DIAG_MEMINFO and INET_DIAG_SKMEMINFO were introduced in Linux
       3.6.

EXAMPLE         top

       The following example program prints inode number, peer's inode
       number, and name of all UNIX domain sockets in the current namespace.

       #include <errno.h>
       #include <stdio.h>
       #include <string.h>
       #include <unistd.h>
       #include <sys/socket.h>
       #include <sys/un.h>
       #include <linux/netlink.h>
       #include <linux/rtnetlink.h>
       #include <linux/sock_diag.h>
       #include <linux/unix_diag.h>

       static int
       send_query(int fd)
       {
           struct sockaddr_nl nladdr = {
               .nl_family = AF_NETLINK
           };
           struct
           {
               struct nlmsghdr nlh;
               struct unix_diag_req udr;
           } req = {
               .nlh = {
                   .nlmsg_len = sizeof(req),
                   .nlmsg_type = SOCK_DIAG_BY_FAMILY,
                   .nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP
               },
               .udr = {
                   .sdiag_family = AF_UNIX,
                   .udiag_states = -1,
                   .udiag_show = UDIAG_SHOW_NAME | UDIAG_SHOW_PEER
               }
           };
           struct iovec iov = {
               .iov_base = &req,
               .iov_len = sizeof(req)
           };
           struct msghdr msg = {
               .msg_name = (void *) &nladdr,
               .msg_namelen = sizeof(nladdr),
               .msg_iov = &iov,
               .msg_iovlen = 1
           };

           for (;;) {
               if (sendmsg(fd, &msg, 0) < 0) {
                   if (errno == EINTR)
                       continue;

                   perror("sendmsg");
                   return -1;
               }

               return 0;
           }
       }

       static int
       print_diag(const struct unix_diag_msg *diag, unsigned int len)
       {
           if (len < NLMSG_LENGTH(sizeof(*diag))) {
               fputs("short response\n", stderr);
               return -1;
           }
           if (diag->udiag_family != AF_UNIX) {
               fprintf(stderr, "unexpected family %u\n", diag->udiag_family);
               return -1;
           }

           struct rtattr *attr;
           unsigned int rta_len = len - NLMSG_LENGTH(sizeof(*diag));
           unsigned int peer = 0;
           size_t path_len = 0;
           char path[sizeof(((struct sockaddr_un *) 0)->sun_path) + 1];

           for (attr = (struct rtattr *) (diag + 1);
                    RTA_OK(attr, rta_len); attr = RTA_NEXT(attr, rta_len)) {
               switch (attr->rta_type) {
               case UNIX_DIAG_NAME:
                   if (!path_len) {
                       path_len = RTA_PAYLOAD(attr);
                       if (path_len > sizeof(path) - 1)
                           path_len = sizeof(path) - 1;
                       memcpy(path, RTA_DATA(attr), path_len);
                       path[path_len] = '\0';
                   }
                   break;

               case UNIX_DIAG_PEER:
                   if (RTA_PAYLOAD(attr) >= sizeof(peer))
                       peer = *(unsigned int *) RTA_DATA(attr);
                   break;
               }
           }

           printf("inode=%u", diag->udiag_ino);

           if (peer)
               printf(", peer=%u", peer);

           if (path_len)
               printf(", name=%s%s", *path ? "" : "@",
                       *path ? path : path + 1);

           putchar('\n');
           return 0;
       }

       static int
       receive_responses(int fd)
       {
           long buf[8192 / sizeof(long)];
           struct sockaddr_nl nladdr = {
               .nl_family = AF_NETLINK
           };
           struct iovec iov = {
               .iov_base = buf,
               .iov_len = sizeof(buf)
           };
           int flags = 0;

           for (;;) {
               struct msghdr msg = {
                   .msg_name = (void *) &nladdr,
                   .msg_namelen = sizeof(nladdr),
                   .msg_iov = &iov,
                   .msg_iovlen = 1
               };

               ssize_t ret = recvmsg(fd, &msg, flags);

               if (ret < 0) {
                   if (errno == EINTR)
                       continue;

                   perror("recvmsg");
                   return -1;
               }
               if (ret == 0)
                   return 0;

               const struct nlmsghdr *h = (struct nlmsghdr *) buf;

               if (!NLMSG_OK(h, ret)) {
                   fputs("!NLMSG_OK\n", stderr);
                   return -1;
               }

               for (; NLMSG_OK(h, ret); h = NLMSG_NEXT(h, ret)) {
                   if (h->nlmsg_type == NLMSG_DONE)
                       return 0;

                   if (h->nlmsg_type == NLMSG_ERROR) {
                       const struct nlmsgerr *err = NLMSG_DATA(h);

                       if (h->nlmsg_len < NLMSG_LENGTH(sizeof(*err))) {
                           fputs("NLMSG_ERROR\n", stderr);
                       } else {
                           errno = -err->error;
                           perror("NLMSG_ERROR");
                       }

                       return -1;
                   }

                   if (h->nlmsg_type != SOCK_DIAG_BY_FAMILY) {
                       fprintf(stderr, "unexpected nlmsg_type %u\n",
                               (unsigned) h->nlmsg_type);
                       return -1;
                   }

                   if (print_diag(NLMSG_DATA(h), h->nlmsg_len))
                       return -1;
               }
           }
       }

       int
       main(void)
       {
           int fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_SOCK_DIAG);

           if (fd < 0) {
               perror("socket");
               return 1;
           }

           int ret = send_query(fd) || receive_responses(fd);

           close(fd);
           return ret;
       }

SEE ALSO         top

       netlink(3), rtnetlink(3), netlink(7), tcp(7)

COLOPHON         top

       This page is part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                            2016-12-07                     SOCK_DIAG(7)

Pages that refer to this page: netlink(7)