你能发布你的配置吗？您是否在CentOS 7上使用Squid并启用了SELinux？执行命令getenforce来找出答案。如果其输出显示Enforcing，则SELinux已启用，您应该与Squid the same way the RedHat documentation specifies进行交互（启动/停止/更改）。
使用Squid，您应该在配置中添加一个新的acl，引用您的Ubuntu服务器IP。
示例：acl ubuntu src 216.128.143.117/32
然后，您应该添加一个新的http_access指令，允许您的acl访问Squid。
示例：http_access allow ubuntu
我有一种感觉，你正在使用一个本地IP地址，所以你必须确保Squid配置为允许来自本地IP的流量。如果你正在添加一个http_access allow all指令（不建议），那么确保它在http_access deny all指令之上，如果它存在的话。
在Ubuntu上，你可以enable an http/s proxy by doing：
export http_proxy="http://{host}:{port}/"用于http代理，以及
export https_proxy="https://{host}:{port}/"用于https代理。
这将把所有http和https请求转发到指定的服务器。
将这些指令添加到users .bashrc文件中，使其对于 that 用户是永久的，或者将它们添加到/etc/environment中，使其在系统范围内是永久的。
如果你还在挣扎，我自己测试了它，并在几分钟内得到它的工作。
我在德克萨斯州达拉斯的Vultr上部署了2台服务器：
一个运行CentOS 7 SELinux，另一个运行Ubuntu 22.04 LTS。
在CentOS服务器上，我做了以下操作：
sudo yum update个
sudo yum install squid个
sudo firewall-cmd --add-port=3128/tcp --permanent个
sudo firewall-cmd --reload个
nano /etc/squid/squid.conf并添加：
acl ubuntu src 216.128.143.117/32和http_access allow ubuntu
然后，我做了systemctl start squid.service
我的squid.conf看起来像这样：

#
# Recommended minimum configuration:
#

# Example rule allowing access from your local networks.
# Adapt to list your (internal) IP networks from where browsing
# should be allowed
##########
acl ubuntu src 216.128.143.117/32
##########
acl localnet src 10.0.0.0/8     # RFC1918 possible internal network
acl localnet src 172.16.0.0/12  # RFC1918 possible internal network
acl localnet src 192.168.0.0/16 # RFC1918 possible internal network
acl localnet src fc00::/7       # RFC 4193 local private network range
acl localnet src fe80::/10      # RFC 4291 link-local (directly plugged) machines

acl SSL_ports port 443
acl Safe_ports port 80          # http
acl Safe_ports port 21          # ftp
acl Safe_ports port 443         # https
acl Safe_ports port 70          # gopher
acl Safe_ports port 210         # wais
acl Safe_ports port 1025-65535  # unregistered ports
acl Safe_ports port 280         # http-mgmt
acl Safe_ports port 488         # gss-http
acl Safe_ports port 591         # filemaker
acl Safe_ports port 777         # multiling http
acl CONNECT method CONNECT

#
# Recommended minimum Access Permission configuration:
#
# Deny requests to certain unsafe ports
http_access deny !Safe_ports

# Deny CONNECT to other than secure SSL ports
http_access deny CONNECT !SSL_ports

# Only allow cachemgr access from localhost
http_access allow localhost manager
http_access deny manager
#
# We strongly recommend the following be uncommented to protect innocent
# web applications running on the proxy server who think the only
# one who can access services on "localhost" is a local user
#http_access deny to_localhost

#
# INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS
#

# Example rule allowing access from your local networks.
# Adapt localnet in the ACL section to list your (internal) IP networks
# from where browsing should be allowed
http_access allow localnet
http_access allow localhost
##########
http_access allow ubuntu
##########
# And finally deny all other access to this proxy
http_access deny all

# Squid normally listens to port 3128
http_port 3128

# Uncomment and adjust the following to add a disk cache directory.
#cache_dir ufs /var/spool/squid 100 16 256

# Leave coredumps in the first cache dir
coredump_dir /var/spool/squid

#
# Add any of your own refresh_pattern entries above these.
#
refresh_pattern ^ftp:           1440    20%     10080
refresh_pattern ^gopher:        1440    0%      1440
refresh_pattern -i (/cgi-bin/|\?) 0     0%      0
refresh_pattern .               0       20%     4320

字符串
在Ubuntu服务器上，我做了：
sudo apt-get update个
export http_proxy="http://216.128.131.111:3128/"个
export https_proxy="https://216.128.131.111:3128/"个
然后我做了curl ipinfo.io/ip，响应是216.128.131.111，我的CentOS服务器IP。