Everything worked fine last time I used Solus, and now I cannot boot because of the error below.
Let's try to solve it without using a live USB.
**Failed to start File System Check on /dev/disk/by-partuuid/5ff8cfe6-53e1-43b1-9275-dc6f24ad812a**
According to the man page,
fsck's error code 4 means "Filesystem errors left uncorrected".
This is not good. It means that the file system is corrupted beyond what is safe to automatically repair on boot, so manual intervention is required.
As the error message on your screen says, you need to manually run
fsck to attempt to fix the errors. You can probably do that from the initramfs root prompt (try
fsck /dev/sda6). If not, you'll need a rescue disk like gparted. IMO, Clonezilla also serves as a good rescue disk - it's got just about every file-system related utility you could possibly need.
Alternatively, since your Linux box is running
systemd, you could interrupt the GRUB boot process and edit the linux kernel's command line to make system perform a forced fsck:
grubtimes out and boots a kernel, press a key to cancel the timeout countdown.
linuxfollowed by a whole bunch of kernel options.
fsck.mode=force fsck.repair=preento the end of that line.
Note: these grub edits are not persistent across reboots. They're temporary one-time changes for this boot session only.
Also note: it's possible that your filesystem is corrupted beyond repair.
fsck will do its best to get the fs back to a consistent state, but it's not magic: it can't repair or restore corrupted data.