# Pynq Build Error -- libxcb

**URL:** <https://discuss.pynq.io/t/pynq-build-error-libxcb/1652>\
**Category:** Support\
**Created:** [August 18, 2020, 10:16am UTC](https://discuss.pynq.io/t/pynq-build-error-libxcb/1652 "2020-08-18T10:16:37Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Sara\_aj](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.pynq.io/sara_aj/32/1194_2.png) [@Sara\_aj](https://discuss.pynq.io/u/Sara_aj)\
**Post date:** [August 18, 2020, 10:16am UTC](https://discuss.pynq.io/t/pynq-build-error-libxcb/1652/1 "2020-08-18T10:16:37Z")

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Hi I got PYNQ build failing several times.  
Specifically near 99% when downloading Ubuntu packages.

Using Petalinux 2019.1 and Ubuntu 2018  
Tried it with Ubuntu 2018, same error  
I used “vagrant up” to create the VM

LOGS: (removing http – because can’t post more than 2 links)

Get:1509 ubuntu-ports bionic/main armhf ssh-import-id all 5.7-0ubuntu1 [10.4 kB]  
Get:1510 ubuntu-ports bionic/main armhf usb-modeswitch-data all 20170806-2 [30.7 kB]  
Get:1511 ubuntu-ports bionic/main armhf usb-modeswitch armhf 2.5.2+repack0-2ubuntu1 [50.7 kB]  
Get:1512 ubuntu-ports bionic/main armhf xserver-xorg-legacy armhf 2:1.19.6-1ubuntu4 [32.4 kB]  
Fetched 673 MB in 56min 7s (200 kB/s)  
E: Failed to fetch [http://ports.ubuntu.com/ubuntu-ports/pool/main/libx/libxcb/libxcb-randr0\_1.13-1\_armhf.deb](http://ports.ubuntu.com/ubuntu-ports/pool/main/libx/libxcb/libxcb-randr0_1.13-1_armhf.deb) Hash Sum mismatch

E: Failed to fetch [http://ports.ubuntu.com/ubuntu-ports/pool/universe/i/isl-0.18/libisl15\_0.18-4\_armhf.deb](http://ports.ubuntu.com/ubuntu-ports/pool/universe/i/isl-0.18/libisl15_0.18-4_armhf.deb) Hash Sum mismatch

E: Some files failed to download  
apt download failed. Exit value: 100  
Makefile:322: recipe for target ‘/workspace/builds/PYNQ/sdbuild/build/bionic.arm.stage1.img’ failed  
make: \*\*\* [/workspace/builds/PYNQ/sdbuild/build/bionic.arm.stage1.img] Error 100

Also, is it possible to restart the build form the same point.  
I have to run the build process again every-time after this error

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<div class="post-metadata">

**Author:** ![rock](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.pynq.io/rock/32/32_2.png) [@rock](https://discuss.pynq.io/u/rock)\
**Post date:** [August 19, 2020, 1:48am UTC](https://discuss.pynq.io/t/pynq-build-error-libxcb/1652/2 "2020-08-19T01:48:06Z")

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Are you behind a proxy or just using home network?

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<div class="post-metadata">

**Author:** ![Sara\_aj](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.pynq.io/sara_aj/32/1194_2.png) [@Sara\_aj](https://discuss.pynq.io/u/Sara_aj)\
**Post date:** [August 19, 2020, 11:17am UTC](https://discuss.pynq.io/t/pynq-build-error-libxcb/1652/3 "2020-08-19T11:17:15Z")

</div>

I am not using Home network, working behind university routers. There is a possibility that there is some proxy issues with routers.

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<div class="post-metadata">

**Author:** ![rock](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.pynq.io/rock/32/32_2.png) [@rock](https://discuss.pynq.io/u/rock)\
**Post date:** [August 19, 2020, 3:21pm UTC](https://discuss.pynq.io/t/pynq-build-error-libxcb/1652/4 "2020-08-19T15:21:02Z")

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Add proxy variable (adjust gateway in the following) to your build machine.

```auto
export HTTP_PROXY=http://gateway:8080
export HTTPS_PROXY=http://gateway:8080
export http_proxy=http://gateway:8080
export https_proxy=http://gateway:8080
export ftp_proxy=http://gateway:8080

```