| SIGSEGV |
Segmentation fault (core dumped) |
A program accessed memory it wasn’t allowed to, and the kernel killed it with SIGSEGV (exit code 139). |
| System has not been booted with systemd |
System has not been booted with systemd as init system (PID 1). Can't operate. |
You ran systemctl inside an environment without systemd as PID 1 — a Docker container or older WSL. |
| Repository does not have a Release file |
E: The repository '...' does not have a Release file |
apt can’t find index files for a source — the repo doesn’t support your Ubuntu/Debian release, the URL is wro… |
| Start request repeated too quickly |
systemd: Start request repeated too quickly / service hit its start limit |
The service crashed and restarted several times in a short period, so systemd stopped trying (StartLimitBurst… |
| cannot execute binary file |
cannot execute binary file: Exec format error |
The program was built for a different CPU architecture or OS — e.g. an x86_64 binary on an ARM machine (Raspb… |
| EACCES |
Linux: Permission denied |
Your user (or the service user) lacks read/write/execute permission on a file, directory or one of its parent… |
| GLIBC_2.xx not found |
/lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.34' not found |
The binary was built on a newer Linux than the one you run it on, and needs a newer glibc than your system ha… |
| Failed to connect to bus |
Failed to connect to bus: No such file or directory (systemctl --user / timedatectl) |
The command needs the D-Bus/systemd bus, which isn’t available in this session — common over su, sudo -u, cro… |
| Setting locale failed |
perl: warning: Setting locale failed / bash: warning: setlocale: LC_ALL: cannot change locale |
Your session asks for a locale (often forwarded by SSH from your Mac/PC) that isn’t generated on the server. |
| Too many levels of symbolic links |
Too many levels of symbolic links (ELOOP) |
A symlink points to itself, directly or through a chain, so path resolution loops. |
| error while loading shared libraries |
error while loading shared libraries: libX.so.N: cannot open shared object file: No such file or directory |
The program needs a shared library (.so) that isn’t installed or isn’t on the loader’s search path. |
| Read-only file system |
Read-only file system (EROFS) — cannot write to disk |
The filesystem is mounted read-only — often because the kernel remounted it after detecting disk errors. |
| Temporary failure in name resolution |
ping: google.com: Temporary failure in name resolution |
The Linux host can’t resolve domain names — no working DNS server is configured or reachable. |
| ssh port 22 Connection refused |
ssh: connect to host x port 22: Connection refused |
The server answered, but nothing is listening on the SSH port — sshd isn’t running, it uses another port, or… |
| client_loop: send disconnect: Broken pipe |
client_loop: send disconnect: Broken pipe (SSH session drops when idle) |
The SSH connection was cut — usually an idle timeout on a NAT router, firewall or the server, sometimes a net… |
| No route to host |
connect: No route to host (EHOSTUNREACH) |
The destination host isn’t reachable — it’s down, on another subnet without routing, or a firewall rejects wi… |
| dpkg lock |
E: Could not get lock /var/lib/dpkg/lock-frontend — is another process using it? |
apt can’t run because another package operation (often automatic updates) holds the dpkg lock. |
| Sub-process /usr/bin/dpkg returned an error code (1) |
E: Sub-process /usr/bin/dpkg returned an error code (1) |
A package’s install/configure script failed, so dpkg aborted. The real error is a few lines above this messag… |
| Cannot allocate memory |
fork: Cannot allocate memory / ENOMEM |
The kernel refused a memory allocation — RAM and swap are exhausted, or overcommit/cgroup limits block it. |
| Job for x.service failed |
Job for nginx.service failed because the control process exited with error code |
systemd tried to start the service, but its start command failed. The real reason is in the service’s status/… |
| sudoers |
user is not in the sudoers file. This incident will be reported. |
Your account isn’t allowed to use sudo. |
| Failed to download metadata for repo |
Error: Failed to download metadata for repo 'appstream' (dnf / yum) |
dnf/yum can’t fetch a repository’s metadata — the mirror is unreachable, the repo URL is dead (CentOS 8 EOL),… |
| ssh port 22 Connection timed out |
ssh: connect to host x port 22: Connection timed out |
SSH packets get no reply — a firewall/security group drops them, the server is off, or the IP is wrong. |
| sudo: unable to resolve host |
sudo: unable to resolve host <hostname>: Name or service not known |
The machine’s hostname isn’t in /etc/hosts (or DNS), so sudo prints this warning — usually after changing the… |
| gzip: stdin: not in gzip format |
gzip: stdin: not in gzip format / tar: Error is not recoverable: exiting now |
The file isn’t actually a gzip archive — often an HTML error page saved by curl/wget, or an archive with a di… |
| Illegal instruction |
Illegal instruction (core dumped) (SIGILL) |
The program used a CPU instruction your processor doesn’t support — typically AVX/AVX2 in prebuilt binaries (… |
| OOM killer |
Killed / Out of memory: Killed process (Linux OOM killer) |
The kernel ran out of memory and killed a process to recover — the program just prints “Killed” (exit code 13… |
| avc: denied |
SELinux is preventing ... / avc: denied { read } for pid=... (permission denied despite correct permissions) |
SELinux blocked the access — file permissions look fine, but the file’s security context or a boolean doesn’t… |
| dpkg was interrupted |
E: dpkg was interrupted, you must manually run 'sudo dpkg --configure -a' to correct the problem |
A previous package operation stopped halfway (closed terminal, reboot, power loss), and apt refuses to contin… |
| Kernel panic - VFS: Unable to mount root fs |
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) |
The kernel booted but couldn’t mount the root filesystem — usually a missing or broken initramfs after a kern… |
| bind() failed (98: Address already in use) |
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use) |
Nginx (or another server) can’t listen on the port because another process already holds it — often Apache, a… |
| REMOTE HOST IDENTIFICATION HAS CHANGED |
WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! (ssh host key changed) |
The server’s SSH host key differs from the one saved in ~/.ssh/known_hosts — usually because the server was r… |
| Argument list too long |
bash: /bin/rm: Argument list too long |
A glob like * expanded to more file names than the kernel allows in one command (ARG_MAX), so the command nev… |
| Network is unreachable |
connect: Network is unreachable (ENETUNREACH) |
The host has no route to the destination network — no default gateway, interface down, or trying IPv6 without… |
| fork: retry: Resource temporarily unavailable |
fork: retry: Resource temporarily unavailable (process/thread limit) |
The user or container hit its maximum number of processes/threads (ulimit -u, pids cgroup), so new processes… |
| wrong fs type, bad option, bad superblock |
mount: wrong fs type, bad option, bad superblock on /dev/sdb1, missing codepage or helper program |
mount couldn’t mount the device — the filesystem type isn’t supported/installed, the partition is wrong, or t… |
| No space left on device (inodes) |
No space left on device, but df shows free space (inodes exhausted) |
The filesystem has run out of inodes — the slots for files — even though there are gigabytes free, usually be… |
| NO_PUBKEY |
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY |
apt can’t verify a repository’s signature because the repo’s signing key isn’t installed (or has expired/rota… |
| held broken packages |
Unmet dependencies / E: Unable to correct problems, you have held broken packages |
apt can’t find a set of package versions that satisfies all dependencies — usually mixed repositories or a pa… |
| UNPROTECTED PRIVATE KEY FILE |
WARNING: UNPROTECTED PRIVATE KEY FILE! Permissions 0644 for 'key.pem' are too open |
SSH refuses to use a private key that other users can read; it must be readable only by you (chmod 600). |
| Disk quota exceeded |
Disk quota exceeded (EDQUOT) |
Your user or group has used its storage quota on this filesystem, even if the disk itself has space. |
| grub rescue unknown filesystem |
error: unknown filesystem. Entering rescue mode... grub rescue> |
GRUB can’t find or read the partition holding its files — common after resizing/deleting partitions or instal… |
| Unit not found |
Failed to start x.service: Unit x.service not found |
systemd has no unit with that name — the package isn’t installed, the name differs on this distro, or a new u… |
| EMFILE |
Too many open files (EMFILE) |
The process hit its file-descriptor limit — sockets, files and pipes all count. |
| target is busy |
umount: target is busy / Device or resource busy |
The filesystem or device can’t be unmounted or removed because a process is still using it. |
| Unable to locate package |
E: Unable to locate package (apt / apt-get install) |
apt can’t find the package name in its package lists — the lists are stale, the repository isn’t enabled, or… |
| Authentication token manipulation error |
passwd: Authentication token manipulation error |
passwd couldn’t update the password — the root filesystem is read-only, /etc/shadow has wrong permissions/att… |
| Too many authentication failures |
Received disconnect: Too many authentication failures |
Your SSH agent offered too many keys before the right one, and the server cut the connection (MaxAuthTries, d… |
| Text file busy |
Text file busy (ETXTBSY) when replacing or running a binary |
You tried to overwrite an executable that is currently running, or run one that is still open for writing. |
| command not found |
bash: command not found |
The shell can’t find an executable with that name in any directory on your PATH. |
| status=203/EXEC |
systemd: Main process exited, code=exited, status=203/EXEC |
systemd couldn’t execute the ExecStart command — the path is wrong, the file isn’t executable, or its interpr… |