ubuntu启动unable to locate package怎么办？

Question

执行安装命令失败:

vmregad@ubuntu:~$ sudo apt-get install python3-pip
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package python3-pip

软件源更新

vmregad@ubuntu:~$ sudo apt update
Ign:1 https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish InRelease        
Ign:2 http://security.ubuntu.com/ubuntu cuttlefish-security InRelease         
Ign:3 https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish-updates InRelease
Err:4 http://security.ubuntu.com/ubuntu cuttlefish-security Release           
  404  Not Found [IP: 91.189.91.38 80]
Ign:5 https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish-backports InRelease
Ign:6 https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish-security InRelease
Err:7 https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish Release
  Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate.  Could not handshake: Error in the certificate verification. [IP: 101.6.15.130 443]
Err:8 https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish-updates Release
  Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate.  Could not handshake: Error in the certificate verification. [IP: 101.6.15.130 443]
Err:9 https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish-backports Release
  Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate.  Could not handshake: Error in the certificate verification. [IP: 101.6.15.130 443]
Err:10 https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish-security Release
  Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate.  Could not handshake: Error in the certificate verification. [IP: 101.6.15.130 443]
Ign:11 http://us.archive.ubuntu.com/ubuntu cuttlefish InRelease
Ign:12 http://us.archive.ubuntu.com/ubuntu cuttlefish-updates InRelease
Ign:13 http://us.archive.ubuntu.com/ubuntu cuttlefish-backports InRelease
Err:14 http://us.archive.ubuntu.com/ubuntu cuttlefish Release
  404  Not Found [IP: 91.189.91.39 80]
Err:15 http://us.archive.ubuntu.com/ubuntu cuttlefish-updates Release
  404  Not Found [IP: 91.189.91.39 80]
Err:16 http://us.archive.ubuntu.com/ubuntu cuttlefish-backports Release
  404  Not Found [IP: 91.189.91.39 80]
Reading package lists... Done
E: The repository 'http://security.ubuntu.com/ubuntu cuttlefish-security Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish-updates Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish-backports Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'https://mirrors.tuna.tsinghua.edu.cn/ubuntu cuttlefish-security Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://us.archive.ubuntu.com/ubuntu cuttlefish Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://us.archive.ubuntu.com/ubuntu cuttlefish-updates Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://us.archive.ubuntu.com/ubuntu cuttlefish-backports Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

软件源信息：
sudo gedit /etc/apt/sources.list

deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ cuttlefish main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ cuttlefish main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ cuttlefish-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ cuttlefish-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ cuttlefish-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ cuttlefish-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ cuttlefish-security main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ cuttlefish-security main restricted universe multiverse

#deb cdrom:[Ubuntu 18.10 _cuttlefish cuttlefish_ - Release amd64 (20181017.3)]/ cuttlefish main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu/ cuttlefish main restricted
# deb-src http://us.archive.ubuntu.com/ubuntu/ cuttlefish main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ cuttlefish-updates main restricted
# deb-src http://us.archive.ubuntu.com/ubuntu/ cuttlefish-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ cuttlefish universe
# deb-src http://us.archive.ubuntu.com/ubuntu/ cuttlefish universe
deb http://us.archive.ubuntu.com/ubuntu/ cuttlefish-updates universe
# deb-src http://us.archive.ubuntu.com/ubuntu/ cuttlefish-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://us.archive.ubuntu.com/ubuntu/ cuttlefish multiverse
# deb-src http://us.archive.ubuntu.com/ubuntu/ cuttlefish multiverse
deb http://us.archive.ubuntu.com/ubuntu/ cuttlefish-updates multiverse
# deb-src http://us.archive.ubuntu.com/ubuntu/ cuttlefish-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ cuttlefish-backports main restricted universe multiverse
# deb-src http://us.archive.ubuntu.com/ubuntu/ cuttlefish-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu cuttlefish partner
# deb-src http://archive.canonical.com/ubuntu cuttlefish partner

deb http://security.ubuntu.com/ubuntu cuttlefish-security main restricted
# deb-src http://security.ubuntu.com/ubuntu cuttlefish-security main restricted
deb http://security.ubuntu.com/ubuntu cuttlefish-security universe
# deb-src http://security.ubuntu.com/ubuntu cuttlefish-security universe
deb http://security.ubuntu.com/ubuntu cuttlefish-security multiverse
# deb-src http://security.ubuntu.com/ubuntu cuttlefish-security multiverse

# This system was installed using small removable media
# (e.g. netinst, live or single CD). The matching "deb cdrom"
# entries were disabled at the end of the installation process.
# For information about how to configure apt package sources,
# see the sources.list(5) manual.

Answer 1

把老的删了，换源先把老的都删了，不是让你增加，是让你替换