Topic: error-message
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SSH's "Host key verification failed" and "REMOTE HOST IDENTIFICATION HAS CHANGED" warnings
OpenSSH refuses to connect and prints 'Host key verification failed' or the larger 'WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!' banner when the server's key does not match what is stored in known_hosts. The article explains why a rebuilt server and an actual attack produce the identical message, and how to tell them apart before running ssh-keygen -R.
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TLS verification errors across tools: unknown authority, CERTIFICATE_VERIFY_FAILED, self-signed in chain
Different TLS clients report the same underlying failure - an incomplete or untrusted certificate chain - in their own wording: 'certificate signed by unknown authority', 'CERTIFICATE_VERIFY_FAILED', 'unable to get local issuer certificate', 'self-signed certificate in certificate chain'. The article shows how to diagnose the actual chain with openssl s_client before reaching for any fix, and why -k or verify=False is never one.
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"Too many open files" (EMFILE) and the file-descriptor limit
EMFILE, reported as 'Too many open files', means a process hit its own limit on simultaneously open file descriptors, documented as RLIMIT_NOFILE. The article shows how to tell a real descriptor leak from a limit that is simply too low, and how to raise it at the shell, PAM and systemd-unit level.
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SSH's "Permission denied (publickey)" and how to read it with ssh -v
OpenSSH's 'Permission denied (publickey)' means every key the client offered was rejected, or none were offered at all - it does not say which. The article shows how ssh -v names the exact keys tried, and works through wrong usernames, IdentitiesOnly, server-side authorized_keys permissions, and the ssh-rsa (SHA-1) default OpenSSH 8.8 disabled.
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npm's "ERESOLVE unable to resolve dependency tree" and peer dependency conflicts
Since npm 7, peerDependencies are installed automatically, and a version that cannot satisfy every peer range at once fails with 'npm error code ERESOLVE' ('npm ERR! code ERESOLVE' before npm 10.6). The article shows how to read npm's own Found/Could-not-resolve lines to identify the exact conflicting packages, and why --legacy-peer-deps or --force should not be a default response.
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"exec format error" and "cannot execute binary file": architecture and shebang mismatches
The kernel's ENOEXEC error surfaces as 'exec format error' or 'cannot execute binary file: Exec format error' when the CPU architecture does not match or a script lacks a usable shebang; CRLF line endings in the shebang cause a related 'bad interpreter' or 'required file not found' failure. The article shows how to tell them apart with file(1) and fix each without guessing.
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Git's "detected dubious ownership in repository" error and the safe.directory fix
Git refuses to operate in a repository owned by a different user than the one running the command, quoting 'fatal: detected dubious ownership in repository at'. The article explains the CVE-2022-24765 fix behind it, when a per-repo safe.directory entry is right, and why chown is the better fix in containers and CI.
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"Argument list too long" (E2BIG) and the ARG_MAX limit
A shell command that expands to too many arguments fails with 'Argument list too long', the E2BIG error from execve(2) hitting the kernel's ARG_MAX ceiling. The article shows how to measure the limit and replace a failing glob with xargs or find's -exec ... + batching instead of trying to quote around it.
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"Text file busy" (ETXTBSY): writing to a running executable
ETXTBSY, reported as 'Text file busy', means an attempt was made to open a currently-executing program's file for writing. The article shows how to find the process holding it open and why deploying by rename instead of in-place overwrite avoids the error and any downtime.
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Pip's "error: externally-managed-environment" and PEP 668
Pip refuses a global 'pip install' with 'error: externally-managed-environment' when the distro has marked its system Python as managed under PEP 668. The article covers what the EXTERNALLY-MANAGED marker means, the venv/pipx/apt fixes in order, and why --break-system-packages is a last resort, not a default.
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"ENOSPC: System limit for number of file watchers reached" and inotify limits
File watchers built on Linux's inotify API fail with 'ENOSPC: System limit for number of file watchers reached' once a per-user kernel limit is exhausted, usually by watching node_modules or similarly large trees. The article covers the two relevant sysctls, how to raise them persistently, and why containers usually share the host's limit.
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"version `GLIBC_2.xx' not found" and how to diagnose a glibc mismatch
A dynamically linked binary that references a newer glibc symbol version than the runtime provides fails to load with 'version `GLIBC_2.xx' not found'. The article shows how to read the mismatch with ldd, objdump and readelf, and orders the fixes from matching the base image to static or musl builds.
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