In a NixOS-like system, it doesn't make sense to hardcode these absolute paths.
They even already use execvp!

diff --git a/usr.sbin/jail/command.c b/usr.sbin/jail/command.c
index 9004b4729fec..669e85ed847e 100644
--- a/usr.sbin/jail/command.c
+++ b/usr.sbin/jail/command.c
@@ -363,7 +363,7 @@ run_command(struct cfjail *j)
 		}
 
 		argv = alloca((8 + argc) * sizeof(char *));
-		argv[0] = _PATH_IFCONFIG;
+		argv[0] = "ifconfig";
 		if ((cs = strchr(val, '|'))) {
 			argv[1] = acs = alloca(cs - val + 1);
 			strlcpy(acs, val, cs - val + 1);
@@ -420,7 +420,7 @@ run_command(struct cfjail *j)
 		}
 
 		argv = alloca((8 + argc) * sizeof(char *));
-		argv[0] = _PATH_IFCONFIG;
+		argv[0] = "ifconfig";
 		if ((cs = strchr(val, '|'))) {
 			argv[1] = acs = alloca(cs - val + 1);
 			strlcpy(acs, val, cs - val + 1);
@@ -454,7 +454,7 @@ run_command(struct cfjail *j)
 
 	case IP_VNET_INTERFACE:
 		argv = alloca(5 * sizeof(char *));
-		argv[0] = _PATH_IFCONFIG;
+		argv[0] = "ifconfig";
 		argv[1] = comstring->s;
 		argv[2] = down ? "-vnet" : "vnet";
 		jidstr = string_param(j->intparams[KP_JID]);
@@ -490,7 +490,7 @@ run_command(struct cfjail *j)
 		if (down) {
 			argv[4] = NULL;
 			argv[3] = argv[1];
-			argv[0] = "/sbin/umount";
+			argv[0] = "umount";
 		} else {
 			if (argc == 4) {
 				argv[7] = NULL;
@@ -503,7 +503,7 @@ run_command(struct cfjail *j)
 				argv[4] = argv[1];
 				argv[3] = argv[0];
 			}
-			argv[0] = _PATH_MOUNT;
+			argv[0] = "mount";
 		}
 		argv[1] = "-t";
 		break;
@@ -521,11 +521,11 @@ run_command(struct cfjail *j)
 		    down ? "devfs" : NULL) < 0)
 			return -1;
 		if (down) {
-			argv[0] = "/sbin/umount";
+			argv[0] = "umount";
 			argv[1] = devpath;
 			argv[2] = NULL;
 		} else {
-			argv[0] = _PATH_MOUNT;
+			argv[0] = "mount";
 			argv[1] = "-t";
 			argv[2] = "devfs";
 			ruleset = string_param(j->intparams[KP_DEVFS_RULESET]);
@@ -552,11 +552,11 @@ run_command(struct cfjail *j)
 		    down ? "fdescfs" : NULL) < 0)
 			return -1;
 		if (down) {
-			argv[0] = "/sbin/umount";
+			argv[0] = "umount";
 			argv[1] = devpath;
 			argv[2] = NULL;
 		} else {
-			argv[0] = _PATH_MOUNT;
+			argv[0] = "mount";
 			argv[1] = "-t";
 			argv[2] = "fdescfs";
 			argv[3] = ".";
@@ -578,11 +578,11 @@ run_command(struct cfjail *j)
 		    down ? "procfs" : NULL) < 0)
 			return -1;
 		if (down) {
-			argv[0] = "/sbin/umount";
+			argv[0] = "umount";
 			argv[1] = devpath;
 			argv[2] = NULL;
 		} else {
-			argv[0] = _PATH_MOUNT;
+			argv[0] = "mount";
 			argv[1] = "-t";
 			argv[2] = "procfs";
 			argv[3] = ".";
@@ -610,7 +610,7 @@ run_command(struct cfjail *j)
 		if ((cs = strpbrk(comstring->s, "!\"$&'()*;<>?[\\]`{|}~")) &&
 		    !(cs[0] == '&' && cs[1] == '\0')) {
 			argv = alloca(4 * sizeof(char *));
-			argv[0] = _PATH_BSHELL;
+			argv[0] = "sh";
 			argv[1] = "-c";
 			argv[2] = comstring->s;
 			argv[3] = NULL;
@@ -763,7 +763,7 @@ run_command(struct cfjail *j)
 		setenv("USER", pwd->pw_name, 1);
 		setenv("HOME", pwd->pw_dir, 1);
 		setenv("SHELL",
-		    *pwd->pw_shell ? pwd->pw_shell : _PATH_BSHELL, 1);
+		    *pwd->pw_shell ? pwd->pw_shell : "sh", 1);
 		if (clean && username && chdir(pwd->pw_dir) < 0) {
 			jail_warnx(j, "chdir %s: %s",
 			    pwd->pw_dir, strerror(errno));