我刚尝试'opam升级'并获得了（最终摘要）：
1 to install | 59 to reinstall | 3 to upgrade | 34 to downgrade | 0 to remove
Do you want to continue ? [Y/n]
降级34包令我感到紧张。为什么要这样做？
它想要降级的软件包的一些示例：
将camlzip.1.05降级为1.04 [google-drive-ocamlfuse所需]
将ezjsonm.0.2.0降级为0.1.0
当然，这让我很紧张，所以我回答'n'。无论如何要解决这个问题？
opam版本是1.1.0。
编辑：我想我也可以发布整个结果：
$ opam upgrade
*The brute-force exploration algorithm timed-out [108 states, 5s].
You might need to add explicit version constraints to your request to get a better answer.*
The following actions will be performed:
- install obuild.0.0.2 [required by mirari]
- downgrade llvm.3.2 to 3.1
- downgrade ocamlfind.1.4.0 to 1.3.3 [required by bitstring, camltc, ezjsonm, fat-filesystem, google-drive-ocamlfuse, merlin, mirage-block-xen, mirage-console-xen, mirari, utop]
- downgrade SPOC.130624 to 121217
- downgrade bitstring.2.0.4 to 2.0.3
- downgrade camlzip.1.05 to 1.04 [required by google-drive-ocamlfuse]
- recompile camomile.0.8.5 [use ocamlfind]
- recompile cmdliner.0.9.2 [use ocamlfind]
- downgrade cryptokit.1.9 to 1.6 [required by google-drive-ocamlfuse]
- recompile dypgen.20120619-1 [use ocamlfind]
- recompile easy-format.1.0.1 [use ocamlfind]
- recompile extlib-compat.1.6.1 [use ocamlfind]
- downgrade fd-send-recv.1.0.1 to 1.0.0 [required by mirari]
- downgrade herelib.109.35.02 to 109.35.00 [required by fat-filesystem, mirage-block-xen, mirage-console-xen]
- recompile ipaddr.1.0.0 [use ocamlfind]
- recompile lablgtk.2.16.0 [use ocamlfind]
- recompile menhir.20130912 [use ocamlfind]
- recompile mirage-types.1.0.0 [use ocamlfind]
- recompile ocamlfuse.2.7.1-cvs [use ocamlfind]
- downgrade ocurl.0.6.0 to 0.5.5 [required by google-drive-ocamlfuse]
- recompile omake.0.9.8.6-0.rc1 [use ocamlfind]
- recompile omd.0.9.0 [use ocamlfind]
- recompile optcomp.1.5 [use ocamlfind]
- downgrade ounit.2.0.0 to 1.1.2 [required by camltc, fat-filesystem, mirage-block-xen, mirage-console-xen]
- recompile parmap.1.0-rc3 [use ocamlfind]
- recompile pipebang.109.28.02 [use ocamlfind]
- recompile re.1.2.1 [use ocamlfind]
- recompile react.0.9.4 [use ocamlfind]
- downgrade res.4.0.4 to 3.2.0 [required by fat-filesystem, mirage-block-xen, mirage-console-xen]
- recompile sqlite3-ocaml.2.0.5 [use ocamlfind]
- recompile ssl.0.4.6 [use ocamlfind]
- downgrade type_conv.109.53.02 to 109.53.00 [required by fat-filesystem, mirage-block-xen, mirage-console-xen]
- recompile ulex.1.1 [use ocamlfind]
- recompile uutf.0.9.3 [use ocamlfind]
- downgrade xmlm.1.2.0 to 1.1.1 [required by google-drive-ocamlfuse]
- downgrade biniou.1.0.6 to 1.0.5 [required by google-drive-ocamlfuse, merlin]
- recompile tuntap.0.7.0 [use ocamlfind]
- recompile ocamldot.1.0 [use ocamlfind]
- recompile ocamlgraph.1.8.3 [use ocamlfind]
- recompile mirage-clock-unix.1.0.0 [use ocamlfind]
- recompile mirage-clock-xen.1.0.0 [use ocamlfind]
- downgrade camlimages.4.1.1 to 4.0.1
- downgrade ocplib-endian.0.4 to 0.3 [required by fat-filesystem, mirage-block-xen, mirage-console-xen]
- downgrade uri.1.3.11 to 1.3.10
- recompile zed.1.2 [use ocamlfind]
- downgrade lwt.2.4.4 to 2.4.3 [required by camltc, fat-filesystem, mirage-block-xen, mirage-console-xen, utop]
- recompile ocamlnet.3.7.3 [use ocamlfind]
- recompile bin_prot.109.53.02 [use ocamlfind]
- recompile comparelib.109.27.02 [use ocamlfind]
- recompile dyntype.0.9.0 [use ocamlfind]
- downgrade fieldslib.109.20.02 to 109.20.00 [required by fat-filesystem, mirage-block-xen, mirage-console-xen]
- recompile pa_ounit.109.53.02 [use ocamlfind]
- downgrade sexplib.109.55.02 to 109.55.00 [required by fat-filesystem, mirage-block-xen, mirage-console-xen]
- downgrade variantslib.109.15.02 to 109.15.00 [required by fat-filesystem, mirage-block-xen, mirage-console-xen]
- recompile jsonm.0.9.1 [use ocamlfind]
- downgrade yojson.1.1.6 to 1.0.3 [required by google-drive-ocamlfuse, merlin]
- downgrade mirari.0.9.7 to 0.9.3
- recompile patoline.0.1 [use ocamlfind]
- upgrade camltc.0.8.1 to 0.8.2
- downgrade lambda-term.1.5 to 1.4 [required by utop]
- recompile cow.0.9.1 [use ocamlfind]
- recompile pa_bench.109.55.02 [use ocamlfind]
- recompile custom_printf.109.27.02 [use ocamlfind]
- recompile typerep.109.55.02 [use ocamlfind]
- downgrade ezjsonm.0.2.0 to 0.1.0
- downgrade gapi-ocaml.0.2.1 to 0.2 [required by google-drive-ocamlfuse]
- downgrade merlin.1.5 to 1.3
- downgrade utop.1.10 to 1.9
- recompile core_kernel.109.55.02 [use ocamlfind]
- downgrade google-drive-ocamlfuse.0.5.2 to 0.4.4
- recompile pa_test.109.53.02 [use ocamlfind]
- recompile core.109.55.02 [use ocamlfind]
- recompile async_core.109.55.02 [use ocamlfind]
- recompile async_unix.109.55.02 [use ocamlfind]
- recompile async_extra.109.55.02 [use ocamlfind]
- recompile async.109.53.02 [use ocamlfind]
- recompile cstruct.1.0.1 [use ocamlfind]
- recompile gen_server.2.0.1 [use ocamlfind]
- upgrade cohttp.0.9.14 to 0.9.16
- recompile io-page-unix.0.9.9 [use ocamlfind]
- recompile io-page-xen.0.9.9 [use ocamlfind]
- recompile mirage-fs-unix.1.0.0 [use ocamlfind]
- downgrade shared-memory-ring.1.0.0 to 0.4.3 [required by mirage-block-xen, mirage-console-xen]
- recompile xenstore.1.2.5 [use ocamlfind]
- recompile cowabloga.0.0.3 [use ocamlfind]
- recompile mirage-http-unix.1.0.0 [use ocamlfind]
- downgrade mirage-block-unix.1.2.0 to 1.1.0 [required by fat-filesystem]
- recompile mirage-net-unix.1.0.0 [use ocamlfind]
- upgrade mirage.1.0.3 to 1.0.4
- recompile mirage-unix.1.0.0 [use ocamlfind]
- recompile mirage-xen.1.0.0 [use ocamlfind]
- downgrade fat-filesystem.0.10.0 to 0.6.2
- recompile mirage-console-unix.1.0.0 [use ocamlfind]
- recompile mirage-tcpip-unix.0.9.5 [use ocamlfind]
- downgrade mirage-block-xen.1.0.0 to 0.4.0
- downgrade mirage-console-xen.1.0.1 to 1.0.0
- recompile mirage-www.1.0.0 [use ocamlfind]
1 to install | 59 to reinstall | 3 to upgrade | 34 to downgrade | 0 to remove
Do you want to continue ? [Y/n]
答案 0 :(得分：4)
长话短说：OPAM有一种非常富有表现力的语言，可以解决几个求解者所理解的依赖关系。默认情况下，OPAM中包含的小而简单的解算器有点像黑客，当被推得太猛时会出现这种可怕的行为。此时，您应该安装一个外部解算器，例如aspcud，这样可以做得更好。
罗伯托·迪·科斯莫（Roberto Di Cosmo）长篇邮件中的更多详细信息，上个月发布在列表中：
答案 1 :(得分：2)
快速修复：为解算器提供更多时间
export OPAMSOLVERTIMEOUT=60
然后再试一次： opam升级
答案 2 :(得分：2)
添加到gasche的答案：描述了外部依赖性解算器的设置on the CUDF Solver Farm
编辑：如果您在使用opam 1.1.1版时遇到此问题，请尝试升级到更新版本。我的similar problem已通过升级解决了。