xenial verification Confirmed the crash and squid's restart: (...) 2017/08/03 13:40:17| pinger: ICMPv6 socket opened 2017/08/03 13:40:18 kid1| storeLateRelease: released 0 objects (issued wget here) 2017/08/03 13:40:28 kid1| cannot change current directory to /var/spool/squid3: (2) No such file or directory 2017/08/03 13:40:28 kid1| Current Directory is / 2017/08/03 13:40:28 kid1| Starting Squid Cache version 3.5.12 for x86_64-pc-linux-gnu... 2017/08/03 13:40:28 kid1| Service Name: squid 2017/08/03 13:40:28 kid1| Process ID 5725 <----- new PID 2017/08/03 13:40:28 kid1| Process Roles: worker wget gave up: $ ftp_proxy=http://xenial-squid-passive-ftp-1560429.lxd:3128/ wget ftp://proftpd.lxd/readme.txt -O /dev/null -t1 --2017-08-03 10:40:22-- ftp://proftpd.lxd/readme.txt Resolving xenial-squid-passive-ftp-1560429.lxd (xenial-squid-passive-ftp-1560429.lxd)... 10.0.100.226 Connecting to xenial-squid-passive-ftp-1560429.lxd (xenial-squid-passive-ftp-1560429.lxd)|10.0.100.226|:3128... connected. Proxy request sent, awaiting response... No data received. Giving up. Installed squid from proposed: (...) Get:1 http://br.archive.ubuntu.com/ubuntu xenial-proposed/main amd64 squid amd64 3.5.12-1ubuntu7.4 [2,310 kB] Get:2 http://br.archive.ubuntu.com/ubuntu xenial-proposed/main amd64 squid-common all 3.5.12-1ubuntu7.4 [176 kB] Fetched 2,486 kB in 0s (11.7 MB/s) (Reading database ... 27771 files and directories currently installed.) Preparing to unpack .../squid_3.5.12-1ubuntu7.4_amd64.deb ... Unpacking squid (3.5.12-1ubuntu7.4) over (3.5.12-1ubuntu7.3) ... Preparing to unpack .../squid-common_3.5.12-1ubuntu7.4_all.deb ... Unpacking squid-common (3.5.12-1ubuntu7.4) over (3.5.12-1ubuntu7.3) ... Processing triggers for systemd (229-4ubuntu19) ... Processing triggers for ureadahead (0.100.0-19) ... Processing triggers for ufw (0.35-0ubuntu2) ... Processing triggers for man-db (2.7.5-1) ... Setting up squid-common (3.5.12-1ubuntu7.4) ... Setting up squid (3.5.12-1ubuntu7.4) ... Skipping profile in /etc/apparmor.d/disable: usr.sbin.squid wget now returns the expected 502 error: $ ftp_proxy=http://xenial-squid-passive-ftp-1560429.lxd:3128/ wget ftp://proftpd.lxd/readme.txt -O /dev/null -t1 --2017-08-03 10:44:58-- ftp://proftpd.lxd/readme.txt Resolving xenial-squid-passive-ftp-1560429.lxd (xenial-squid-passive-ftp-1560429.lxd)... 10.0.100.226 Connecting to xenial-squid-passive-ftp-1560429.lxd (xenial-squid-passive-ftp-1560429.lxd)|10.0.100.226|:3128... connected. Proxy request sent, awaiting response... 502 Bad Gateway 2017-08-03 10:44:58 ERROR 502: Bad Gateway. And squid just logs the attempt, with no crash: ==> /var/log/squid/access.log <== 1501767898.437 14 10.0.100.1 TCP_MISS/502 4356 GET ftp://proftpd.lxd/readme.txt - HIER_DIRECT/10.0.100.227 text/html If I allow passive ftp on proftpd, then the file can be fetched: $ ftp_proxy=http://xenial-squid-passive-ftp-1560429.lxd:3128/ wget ftp://proftpd.lxd/readme.txt -O /dev/null -t1 --2017-08-03 10:47:06-- ftp://proftpd.lxd/readme.txt Resolving xenial-squid-passive-ftp-1560429.lxd (xenial-squid-passive-ftp-1560429.lxd)... 10.0.100.226 Connecting to xenial-squid-passive-ftp-1560429.lxd (xenial-squid-passive-ftp-1560429.lxd)|10.0.100.226|:3128... connected. Proxy request sent, awaiting response... 200 Gatewaying Length: unspecified [text/plain] Saving to: ‘/dev/null’ /dev/null [ <=> ] 7 --.-KB/s in 0s 2017-08-03 10:47:06 (328 KB/s) - ‘/dev/null’ saved [7] squid: 1501768026.900 16 10.0.100.1 TCP_MISS/200 422 GET ftp://proftpd.lxd/readme.txt - HIER_DIRECT/10.0.100.227 text/plain proftpd (no 501 error for the EPSV command): xenial-squid-passive-ftp-1560429.lxd UNKNOWN - [03/Aug/2017:13:47:06 +0000] "USER anonymous" 331 - xenial-squid-passive-ftp-1560429.lxd UNKNOWN ftp [03/Aug/2017:13:47:06 +0000] "PASS (hidden)" 230 - xenial-squid-passive-ftp-1560429.lxd UNKNOWN ftp [03/Aug/2017:13:47:06 +0000] "TYPE A" 200 - xenial-squid-passive-ftp-1560429.lxd UNKNOWN ftp [03/Aug/2017:13:47:06 +0000] "MDTM readme.txt" 213 - xenial-squid-passive-ftp-1560429.lxd UNKNOWN ftp [03/Aug/2017:13:47:06 +0000] "EPSV 1" 229 - xenial-squid-passive-ftp-1560429.lxd UNKNOWN ftp [03/Aug/2017:13:47:06 +0000] "RETR readme.txt" 226 6 xenial-squid-passive-ftp-1560429.lxd UNKNOWN ftp [03/Aug/2017:13:47:06 +0000] "QUIT" 221 -