diff --git a/criu/cr-service.c b/criu/cr-service.c
index f9844570a..219a98624 100644
--- a/criu/cr-service.c
+++ b/criu/cr-service.c
@@ -37,6 +37,7 @@
 #include "setproctitle.h"
 
 #include "cr-errno.h"
+#include "namespaces.h"
 
 unsigned int service_sk_ino = -1;
 
@@ -373,6 +374,11 @@ static int setup_opts_from_req(int sk, CriuOpts *req)
 			goto err;
 	}
 
+	for (i = 0; i < req->n_join_ns; i++) {
+		if (join_ns_add(req->join_ns[i]->ns, req->join_ns[i]->ns_file, req->join_ns[i]->extra_opt))
+			goto err;
+	}
+
 	if (req->n_inherit_fd && !opts.swrk_restore) {
 		pr_err("inherit_fd is not allowed in standalone service\n");
 		goto err;
@@ -472,6 +478,9 @@ static int setup_opts_from_req(int sk, CriuOpts *req)
 		}
 	}
 
+	if (check_namespace_opts())
+		goto err;
+
 	return 0;
 
 err:
diff --git a/criu/crtools.c b/criu/crtools.c
index 4a6dbffb4..f2043ce16 100644
--- a/criu/crtools.c
+++ b/criu/crtools.c
@@ -36,6 +36,7 @@
 #include "cr-service.h"
 #include "plugin.h"
 #include "mount.h"
+#include "namespaces.h"
 #include "cgroup.h"
 #include "cpu.h"
 #include "action-scripts.h"
@@ -58,6 +59,7 @@ void init_opts(void)
 	INIT_LIST_HEAD(&opts.ext_unixsk_ids);
 	INIT_LIST_HEAD(&opts.veth_pairs);
 	INIT_LIST_HEAD(&opts.ext_mounts);
+	INIT_LIST_HEAD(&opts.join_ns);
 	INIT_LIST_HEAD(&opts.inherit_fds);
 	INIT_LIST_HEAD(&opts.external);
 	INIT_LIST_HEAD(&opts.new_cgroup_roots);
@@ -71,6 +73,29 @@ void init_opts(void)
 	opts.empty_ns = 0;
 }
 
+static int parse_join_ns(const char *ptr)
+{
+	char *aux, *ns_file, *extra_opts = NULL;
+
+	aux = strchr(ptr, ':');
+	if (aux == NULL)
+		return -1;
+	*aux = '\0';
+
+	ns_file = aux + 1;
+	aux = strchr(ns_file, ',');
+	if (aux != NULL) {
+		*aux = '\0';
+		extra_opts = aux + 1;
+	} else {
+		extra_opts = NULL;
+	}
+	if (join_ns_add(ptr, ns_file, extra_opts))
+		return -1;
+
+	return 0;
+}
+
 static int parse_cpu_cap(struct cr_options *opts, const char *optarg)
 {
 	bool inverse = false;
@@ -190,7 +215,7 @@ int main(int argc, char *argv[], char *envp[])
 	int log_level = LOG_UNSET;
 	char *imgs_dir = ".";
 	char *work_dir = NULL;
-	static const char short_opts[] = "dSsRf:F:t:p:hcD:o:v::x::Vr:jlW:L:M:";
+	static const char short_opts[] = "dSsRf:F:t:p:hcD:o:v::x::Vr:jJ:lW:L:M:";
 	static struct option long_opts[] = {
 		{ "tree",			required_argument,	0, 't'	},
 		{ "pid",			required_argument,	0, 'p'	},
@@ -205,6 +230,7 @@ int main(int argc, char *argv[], char *envp[])
 		{ "images-dir",			required_argument,	0, 'D'	},
 		{ "work-dir",			required_argument,	0, 'W'	},
 		{ "log-file",			required_argument,	0, 'o'	},
+		{ "join-ns",			required_argument,	0, 'J'	},
 		{ "root",			required_argument,	0, 'r'	},
 		{ USK_EXT_PARAM,		optional_argument,	0, 'x'	},
 		{ "help",			no_argument,		0, 'h'	},
@@ -338,6 +364,10 @@ int main(int argc, char *argv[], char *envp[])
 		case 'o':
 			opts.output = optarg;
 			break;
+		case 'J':
+			if (parse_join_ns(optarg))
+				goto bad_arg;
+			break;
 		case 'v':
 			if (log_level == LOG_UNSET)
 				log_level = 0;
@@ -552,6 +582,11 @@ int main(int argc, char *argv[], char *envp[])
 		}
 	}
 
+	if (check_namespace_opts()) {
+		pr_msg("Error: namespace flags confict\n");
+		return 1;
+	}
+
 	if (!opts.restore_detach && opts.restore_sibling) {
 		pr_msg("--restore-sibling only makes sense with --restore-detach\n");
 		return 1;
@@ -793,6 +828,12 @@ usage:
 "  --empty-ns {net}\n"
 "                        Create a namespace, but don't restore its properies.\n"
 "                        An user will retore them from action scripts.\n"
+"  -J|--join-ns NS:PID|NS_FILE[,EXTRA_OPTS]\n"
+"			Join exist namespace and restore process in it.\n"
+"			Namespace can be specified in pid or file path format.\n"
+"			    --join-ns net:12345 or --join-ns net:/foo/bar.\n"
+"			Extra_opts is optional, for now only user namespace support:\n"
+"			    --join-ns user:PID,UID,GID to specify uid and gid.\n"
 "Check options:\n"
 "  without any arguments, \"criu check\" checks availability of absolutely required\n"
 "  kernel features; if any of these features is missing dump and restore will fail\n"
diff --git a/criu/include/cr_options.h b/criu/include/cr_options.h
index 253aadb3f..4fa709425 100644
--- a/criu/include/cr_options.h
+++ b/criu/include/cr_options.h
@@ -81,6 +81,7 @@ struct cr_options {
 	struct list_head	ext_mounts;
 	struct list_head	inherit_fds;
 	struct list_head	external;
+	struct list_head	join_ns;
 	char			*libdir;
 	bool			use_page_server;
 	unsigned short		port;
diff --git a/criu/include/namespaces.h b/criu/include/namespaces.h
index e7931ec89..15a514a98 100644
--- a/criu/include/namespaces.h
+++ b/criu/include/namespaces.h
@@ -3,6 +3,7 @@
 
 #include "compiler.h"
 #include "files.h"
+#include "list.h"
 
 #ifndef CLONE_NEWNS
 #define CLONE_NEWNS	0x00020000
@@ -36,6 +37,7 @@
 
 /* Nested namespaces are supported only for these types */
 #define CLONE_SUBNS	(CLONE_NEWNS)
+#define EXTRA_SIZE	20
 
 struct ns_desc {
 	unsigned int	cflag;
@@ -43,6 +45,24 @@ struct ns_desc {
 	size_t		len;
 };
 
+struct user_ns_extra {
+	char	*uid;
+	char	*gid;
+};
+
+/* struct join_ns is used for storing parameters specified by --join-ns */
+struct join_ns {
+	struct list_head	list;
+	char			*ns_file;
+	struct ns_desc		*nd;	/* namespace descriptor */
+	int			ns_fd;
+	/* extra options of --join-ns, like uid&gid in user namespace */
+	union {
+		struct user_ns_extra	user_extra;
+		char			*common_extra;
+	} extra_opts;
+};
+
 enum ns_type {
 	NS_UNKNOWN = 0,
 	NS_CRIU,
@@ -124,6 +144,8 @@ extern gid_t userns_gid(gid_t gid);
 
 extern int dump_user_ns(pid_t pid, int ns_id);
 extern void free_userns_maps(void);
+extern int join_ns_add(const char *type, char *ns_file, char *extra_opts);
+extern int check_namespace_opts(void);
 
 typedef int (*uns_call_t)(void *arg, int fd, pid_t pid);
 /*
diff --git a/criu/namespaces.c b/criu/namespaces.c
index 260137c19..ce68d4d62 100644
--- a/criu/namespaces.c
+++ b/criu/namespaces.c
@@ -10,8 +10,12 @@
 #include <signal.h>
 #include <sched.h>
 #include <sys/capability.h>
+#include <sys/stat.h>
+#include <limits.h>
+#include <errno.h>
 
 #include "rst-malloc.h"
+#include "cr_options.h"
 #include "imgset.h"
 #include "uts_ns.h"
 #include "ipc_ns.h"
@@ -35,6 +39,147 @@ static struct ns_desc *ns_desc_array[] = {
 	&cgroup_ns_desc,
 };
 
+static unsigned int join_ns_flags;
+
+int check_namespace_opts(void)
+{
+	errno = 22;
+	if (join_ns_flags & opts.rst_namespaces_flags) {
+		pr_perror("Conflict flags: -join-ns and -namespace");
+		return -1;
+	}
+	if (join_ns_flags & opts.empty_ns) {
+		pr_perror("Conflict flags: -join-ns and -empty-ns");
+		return -1;
+	}
+	errno = 0;
+	return 0;
+}
+
+static int check_int_str(char *str)
+{
+	char *endptr;
+	long val;
+
+	if (str == NULL)
+		return 0;
+
+	if (*str == '\0') {
+		str = NULL;
+		return 0;
+	}
+
+	errno = 22;
+	val = strtol(str, &endptr, 10);
+	if ((errno == ERANGE) || (endptr == str)
+			|| (*endptr != '\0')
+			|| (val < 0) || (val > 65535)) {
+		str = NULL;
+		return -1;
+	}
+
+	errno = 0;
+	return 0;
+}
+
+static int check_ns_file(char *ns_file)
+{
+	int pid, ret, proc_dir;
+
+	if (!check_int_str(ns_file)) {
+		pid = atoi(ns_file);
+		if (pid <= 0) {
+			pr_perror("Invalid join_ns pid %s", ns_file);
+			return -1;
+		}
+		proc_dir = open_pid_proc(pid);
+		if (proc_dir < 0) {
+			pr_perror("Invalid join_ns pid: /proc/%s not found", ns_file);
+			return -1;
+		}
+		return 0;
+	}
+
+	ret = access(ns_file, 0);
+	if (ret < 0) {
+		pr_perror("Can't access join-ns file: %s", ns_file);
+		return -1;
+	}
+	return 0;
+}
+
+static int set_user_extra_opts(struct join_ns *jn, char *extra_opts)
+{
+	char *uid, *gid, *aux;
+
+	if (extra_opts == NULL) {
+		jn->extra_opts.user_extra.uid = NULL;
+		jn->extra_opts.user_extra.gid = NULL;
+		return 0;
+	}
+
+	uid = extra_opts;
+	aux = strchr(extra_opts, ',');
+	if (aux == NULL) {
+		gid = NULL;
+	} else {
+		*aux = '\0';
+		gid = aux + 1;
+	}
+
+	if (check_int_str(uid) || check_int_str(gid))
+		return -1;
+
+	jn->extra_opts.user_extra.uid = uid;
+	jn->extra_opts.user_extra.gid = gid;
+
+	return 0;
+}
+
+int join_ns_add(const char *type, char *ns_file, char *extra_opts)
+{
+	struct join_ns *jn;
+
+	jn = xmalloc(sizeof(*jn));
+	if (!jn)
+		return -1;
+
+	if (check_ns_file(ns_file))
+		return -1;
+
+	jn->ns_file = ns_file;
+	if (!strncmp(type, "net", 4)) {
+		jn->nd = &net_ns_desc;
+		join_ns_flags |= CLONE_NEWNET;
+	} else if (!strncmp(type, "uts", 4)) {
+		jn->nd = &uts_ns_desc;
+		join_ns_flags |= CLONE_NEWUTS;
+	} else if (!strncmp(type, "ipc", 4)) {
+		jn->nd = &ipc_ns_desc;
+		join_ns_flags |= CLONE_NEWIPC;
+	} else if (!strncmp(type, "pid", 4)) {
+		pr_perror("join-ns pid namespace not supported\n");
+		return -1;
+	} else if (!strncmp(type, "user", 5)) {
+		jn->nd = &user_ns_desc;
+		if (set_user_extra_opts(jn, extra_opts)) {
+			pr_perror("invalid user namespace extra_opts %s\n", extra_opts);
+			return -1;
+		}
+		join_ns_flags |= CLONE_NEWUSER;
+	} else if (!strncmp(type, "mnt", 4)) {
+		jn->nd = &mnt_ns_desc;
+		join_ns_flags |= CLONE_NEWNS;
+	} else {
+		pr_perror("invalid namespace type %s\n", type);
+		return -1;
+	}
+
+	list_add_tail(&jn->list, &opts.join_ns);
+	pr_info("Added %s:%s join namespace\n", type, ns_file);
+	return 0;
+}
+
 static unsigned int parse_ns_link(char *link, size_t len, struct ns_desc *d)
 {
 	unsigned long kid = 0;
diff --git a/images/rpc.proto b/images/rpc.proto
index fac4b9fa0..9ece4dabb 100644
--- a/images/rpc.proto
+++ b/images/rpc.proto
@@ -15,6 +15,12 @@ message ext_mount_map {
 	required string		val	= 2;
 };
 
+message join_namespace {
+	required string		ns		= 1;
+	required string		ns_file		= 2;
+	optional string		extra_opt	= 3;
+}
+
 message inherit_fd {
 	required string		key	= 1;
 	required int32		fd	= 2;
@@ -90,6 +96,7 @@ message criu_opts {
 	repeated string			irmap_scan_paths = 36;
 	repeated string			external	= 37;
 	optional uint32			empty_ns	= 38;
+	repeated join_namespace		join_ns		= 39;
 }
 
 message criu_dump_resp {