# Utop not installing

**URL:** https://discuss.ocaml.org/t/utop-not-installing/4347
**Category:** Learning
**Created:** [September 11, 2019, 12:16am UTC](https://discuss.ocaml.org/t/utop-not-installing/4347 "2019-09-11T00:16:38Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![yash26](https://avatars.discourse-cdn.com/v4/letter/y/eb9ed0/32.png) [@yash26](https://discuss.ocaml.org/u/yash26)
#### Post date: [September 11, 2019, 12:16am UTC](https://discuss.ocaml.org/t/utop-not-installing/4347/1 "2019-09-11T00:16:38Z")

</div>

```auto
Yashwanths-MacBook-Pro:~ yashwanthreddy$ opam install lwt
The following actions will be performed:
  ∗ install lwt 4.3.0

<><> Gathering sources ><><><><><><><><><><><><><><><><><><><><><><><><><><> 🐫 
[lwt.4.3.0] found in cache

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><> 🐫 
[ERROR] The compilation of lwt failed at "/Users/yashwanthreddy/.opam/opam-init/hooks/sandbox.sh build dune build -p lwt -j 7".

#=== ERROR while compiling lwt.4.3.0 ==========================================#
# context 2.0.5 | macos/x86_64 | ocaml-system.4.08.1 | https://opam.ocaml.org#852124c0
# path ~/.opam/default/.opam-switch/build/lwt.4.3.0
# command ~/.opam/opam-init/hooks/sandbox.sh build dune build -p lwt -j 7
# exit-code 1
# env-file ~/.opam/log/lwt-50424-ffb3fd.env
# output-file ~/.opam/log/lwt-50424-ffb3fd.out
### output ###
# [...]
# #include <stdlib.h>
# ^ ~~~~~~~~~
# 1 error generated.
# ocamlc src/unix/lwt_libev_stubs.o (exit 2)
# (cd _build/default/src/unix && /usr/local/bin/ocamlc.opt -g -I /Users/yashwanthreddy/.opam/default/lib/bytes -I /Users/yashwanthreddy/.opam/default/lib/mmap -I /Users/yashwanthreddy/.opam/default/lib/ocplib-endian -I /Users/yashwanthreddy/.opam/default/lib/result -I /Users/yashwanthreddy/.opam/default/lib/seq -I /usr/local/lib/ocaml/threads -I ../core -ccopt -I. -ccopt -g -o lwt_libev_stubs.o[...]
# In file included from lwt_libev_stubs.c:9:
# In file included from ./lwt_unix.h:11:
# In file included from /usr/local/lib/ocaml/caml/mlvalues.h:23:
# /usr/local/lib/ocaml/caml/misc.h:29:10: fatal error: 'stdlib.h' file not found
# #include <stdlib.h>
# ^ ~~~~~~~~~
# 1 error generated.

<><> Error report <><><><><><><><><><><><><><><><><><><><><><><><><><><><><> 🐫 
┌─ The following actions failed
│ λ build lwt 4.3.0
└─ 
╶─ No changes have been performed

<><> lwt.4.3.0 troubleshooting ><><><><><><><><><><><><><><><><><><><><><><> 🐫 
=> Lwt 5.0.0 will make some breaking changes in November 2019. See
     https://github.com/ocsigen/lwt/issues/584
Yashwanths-MacBook-Pro:~ yashwanthreddy$ 

```

Please let me know what is the issue.

---

<div class="post-metadata">

### Author: ![dbuenzli](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/dbuenzli/32/18_2.png) [@dbuenzli](https://discuss.ocaml.org/u/dbuenzli)
#### Post date: [September 11, 2019, 7:03am UTC](https://discuss.ocaml.org/t/utop-not-installing/4347/2 "2019-09-11T07:03:27Z")

</div>

There seem to be a problem with your C environment. What happens if you:

```auto
cd /tmp
echo "#include <stdlib.h>" > a.c
opam exec -- cc -c a.c

```