strace log from my previous message, apologies.

I guess, the issue is because fcgiwrap process environment PATH only
contains /gnu/store/…-shadow-4.5/sbin which doesn't include gzip.

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$ sudo strace -s 128 -p 457
strace: Process 457 attached
accept(0, {sa_family=AF_INET, sin_port=htons(57088), sin_addr=inet_addr("127.0.0.1")}, [112->16]) = 3
setsockopt(3, SOL_TCP, TCP_NODELAY, [1], 4) = 0
read(3, "\1\1\0\1\0\10\0\0\0\1\0\0\0\0\0\0\1\4\0\1\1!\7\0\17FSCRIPT_FILENAME/gnu/store/27ki0l76vn23698caynfknbcnqf5jag0-cgit-1.1/lib/cgit/cgit.cgi\t&PATH_INFO/guix/"..., 8192) = 336
pipe([4, 5])                            = 0
pipe([6, 7])                            = 0
pipe([8, 9])                            = 0
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7ff3f0dc4e10) = 12762
close(4)                                = 0
close(7)                                = 0
close(9)                                = 0
close(5)                                = 0
select(9, [6 8], NULL, NULL, NULL)      = 1 (in [8])
read(8, "[cgit] Unable to lock slot /var/cache/cgit/8a300000.lock: Permission denied (13)\n", 4096) = 81
write(2, "[cgit] Unable to lock slot /var/cache/cgit/8a300000.lock: Permission denied (13)\n", 81) = 81
select(9, [6 8], NULL, NULL, NULL)      = 1 (in [6])
read(6, "Content-Type: application/x-gzip; charset=UTF-8\nContent-Disposition: inline; filename=\"guix-0.13.0.tar.gz\"\n", 4096) = 107
select(9, [6 8], NULL, NULL, NULL)      = 1 (in [6])
read(6, "Last-Modified: Fri, 01 Dec 2017 11:42:10 GMT\nExpires: Fri, 01 Dec 2017 11:47:10 GMT\nETag: \"99d1ec5989eae66719fb968f41560f2879707"..., 4096) = 134
select(9, [6 8], NULL, NULL, NULL)      = 1 (in [8])
read(8, "fatal: Unable to exec subprocess gzip: No such file or directory\n", 4096) = 65
write(2, "fatal: Unable to exec subprocess gzip: No such file or directory\n", 65) = 65
select(9, [6 8], NULL, NULL, NULL)      = 2 (in [6 8])
read(6, "", 4096)                       = 0
close(6)                                = 0
read(8, "", 4096)                       = 0
close(8)                                = 0
write(3, "\1\6\0\1\0\367\1\0Content-Type: application/x-gzip; charset=UTF-8\r\nContent-Disposition: inline; filename=\"guix-0.13.0.tar.gz\"\r\nLast-Modifi"..., 280) = 280
shutdown(3, SHUT_WR)                    = 0
poll([{fd=3, events=POLLIN}], 1, 2000)  = 1 ([{fd=3, revents=POLLIN|POLLHUP}])
read(3, "", 1024)                       = 0
close(3)                                = 0
accept(0,   C-c C-cstrace: Process 457 detached
 <detached ...>
--8<---------------cut here---------------end--------------->8---

--8<---------------cut here---------------start------------->8---
/proc/457$ sudo cat environ
HOME=/
TERM=linux
BOOT_IMAGE=/gnu/store/nrhx7jf33zqxmbw832bpxyrnc0k3lrnq-linux-libre-4.14.2/bzImage --root=magnolia-root --system=/gnu/store/mqwc1vmlnx076aka7gn8bi89hmj6v3pq-system --load=/gnu/store/mqwc1vmlnx076aka7gn8bi89hmj6v3pq-system/boot
PATH=/gnu/store/a8arlhcrf70113zw7b3qrwqbqfq2hgj6-shadow-4.5/sbin
--8<---------------cut here---------------end--------------->8---

Thanks,
Oleg.