Why does this pipe not end when the las process dies (zombie)?

I have a script run and monitored by svscan/supervise. When the last luces-hf/run: #!/bin/bash set -v export http_proxy=[redacted] curl -N -s https://[redacted] |\ grep --line-buffered "event" | http_proxy='' xargs -n 1 luces.sh It seems that when the script launches luces.sh and the script hangs and remains zombie, then the whole pipe remains running. I would like it to fail, so that the script finishes and gets restarted by supervise. This is the process tree: 24788 ? Ss 0:00 /bin/sh /usr/bin/svscanboot 24790 ? S 0:01 \_ svscan /etc/service 24794 ? S 0:00 | \_ supervise luces-hf 29876 ? S 0:00 | | \_ /bin/bash ./run 29877 ? S 0:00 | | \_ curl -N -s https://[redacted][long request never endind. server sent events one line at a time] 29878 ? S 0:00 | | \_ grep --line-buffered event 29879 ? S 0:00 | | \_ xargs -n 1 luces.sh 5885 ? Z 0:00 | | \_ [luces.sh] **EDIT** : luces.shdoes three http requests using curl **EDIT** : strace output for the xargs command in the script: execve("/usr/bin/xargs", ["xargs", "-n", "1", "luces.sh"], [/* 6 vars */]) = 0 brk(0) = 0x1d07000 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fad73c49000 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory) open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0644, st_size=43357, ...}) = 0 mmap(NULL, 43357, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fad73c3e000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320\37\2\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0755, st_size=1840928, ...}) = 0 mmap(NULL, 3949248, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fad73664000 mprotect(0x7fad7381f000, 2093056, PROT_NONE) = 0 mmap(0x7fad73a1e000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1ba000) = 0x7fad73a1e000 mmap(0x7fad73a24000, 17088, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fad73a24000 close(3) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fad73c3d000 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fad73c3b000 arch_prctl(ARCH_SET_FS, 0x7fad73c3b740) = 0 mprotect(0x7fad73a1e000, 16384, PROT_READ) = 0 mprotect(0x609000, 4096, PROT_READ) = 0 mprotect(0x7fad73c4b000, 4096, PROT_READ) = 0 munmap(0x7fad73c3e000, 43357) = 0 brk(0) = 0x1d07000 brk(0x1d28000) = 0x1d28000 getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0 getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0 mmap(NULL, 135168, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fad73c1a000 rt_sigaction(SIGCHLD, {SIG_DFL, [CHLD], SA_RESTORER|SA_RESTART, 0x7fad7369ad40}, {SIG_DFL, [], 0}, 8) = 0 fstat(0, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fad73c48000 read(0, "event: HF\n", 4096) = 10 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fad73c3ba10) = 16952 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 16952 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=16952, si_status=0, si_utime=0, si_stime=0} --- clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fad73c3ba10) = 16968 read(0, 0x7fad73c48000, 4096) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=16968, si_status=0, si_utime=0, si_stime=0} --- read(0, "event: HF\n", 4096) = 10 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 16968 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fad73c3ba10) = 17023 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 17023 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=17023, si_status=0, si_utime=0, si_stime=0} --- clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fad73c3ba10) = 17040 read(0, 0x7fad73c48000, 4096) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=17040, si_status=0, si_utime=0, si_stime=0} --- read(0, "event: HF\n", 4096) = 10 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 17040 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fad73c3ba10) = 17065 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 17065 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=17065, si_status=0, si_utime=0, si_stime=0} --- clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fad73c3ba10) = 17087 read(0, 0x7fad73c48000, 4096) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=17087, si_status=0, si_utime=0, si_stime=0} --- read(0, "event: HF\n", 4096) = 10 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 17087 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fad73c3ba10) = 17127 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 17127 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=17127, si_status=0, si_utime=0, si_stime=0} --- clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fad73c3ba10) = 17147 read(0, 0x7fad73c48000, 4096) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=17147, si_status=0, si_utime=0, si_stime=0} --- read(0, "event: HF\n", 4096) = 10 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 17147 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fad73c3ba10) = 17274 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 17274 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=17274, si_status=0, si_utime=0, si_stime=0} --- clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fad73c3ba10) = 17293 read(0, 0x7fad73c48000, 4096) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=17293, si_status=0, si_utime=0, si_stime=0} ---