Ubuntu 23.04中snapd无法挂载squashfs镜像导致无法安装snap包的问题求助

Hey，我看你在Ubuntu 23.04上安装snap包时碰到了挂载squashfs镜像的问题，这确实会导致snapd没法正常工作。先把你的问题细节整理出来，再给你几个排查和解决的方向：

你遇到的错误场景 #

执行安装命令：

sudo snap install hello-world

输入密码后触发报错：

[sudo] password for noax:

error: system does not fully support snapd: cannot mount squashfs image using "squashfs": ----- mount: /tmp/syscheck-mountpoint-1214103833: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error.
dmesg(1) may have more information after failed mount system call.
-----

你的系统环境 #

内核版本信息：

noax@noax:~$ uname -a
Linux noax 6.2.0-20-generic #20-Ubuntu SMP PREEMPT_DYNAMIC Thu Apr  6 07:48:48 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

dmesg中的相关错误日志：

0.270982] SELinux: CONFIG_SECURITY_SELINUX_CHECKREQPROT_VALUE is non-zero.  This is deprecated and will be rejected in a future kernel release.
[    0.270999] SELinux: https://github.com/SELinuxProject/selinux-kernel/wiki/DEPRECATE-checkreqprot
[    0.502251] ACPI Error: Needed type [Reference], found [Integer] (ptrval) (20221020/exresop-66)
[    0.502251] ACPI Error: AE_AML_OPERAND_TYPE, While resolving operands for [Store] (20221020/dswexec-433)
[    0.502251] ACPI Error: Aborting method _PR.CPU0._PDC due to previous error (AE_AML_OPERAND_TYPE) (20221020/psparse-529)
3.498852] mmc0: error -110 whilst initialising SD card
15.063000] usb 3-6: 1:1: cannot get freq at ep 0x1
20.189003] usb 3-6: 1:1: cannot get freq at ep 0x1

排查和解决步骤 #

Snap依赖squashfs文件系统和loop设备来运行，所以问题大概率出在这两个组件上，按以下步骤尝试修复：

1. 安装内核额外模块包
   Ubuntu默认内核可能没有预装squashfs的模块，安装对应内核版本的额外模块包：

sudo apt update && sudo apt install linux-modules-extra-$(uname -r)

2. 手动加载必要模块
   安装完成后，手动加载squashfs和loop模块：

sudo modprobe squashfs
sudo modprobe loop

3. 重启snapd服务
   让snapd重新加载配置：

sudo systemctl restart snapd

4. 再次尝试安装snap包
   现在重新执行安装命令，看是否能正常运行：

sudo snap install hello-world

额外说明 #

dmesg里的SELinux警告、ACPI错误以及SD卡/USB相关报错，和当前snap挂载问题无关，可以暂时忽略。如果上述步骤无效，再考虑重装snapd：

sudo apt purge snapd && sudo apt install snapd

备注：内容来源于stack exchange，提问作者yop