OhSudo — new Linux articlesNew Linux articles from OhSudo: practical fixes for DevOps engineers, SysAdmins and IT folks.https://ohsudo.com/en-usSELinux "avc: denied": read the denial, then fix the label, the boolean or the porthttps://ohsudo.com/articles/selinux-avc-denied/https://ohsudo.com/articles/selinux-avc-denied/Fix SELinux "avc: denied" on RHEL, Rocky and AlmaLinux: read the AVC line, then fix file labels with restorecon and semanage, booleans with setsebool, or ports.Sun, 15 Nov 2026 00:00:00 GMTLinuxselinuxrhelrocky-linuxalmalinuxnginxsecuritytroubleshootingcontact@ohsudo.com (OhSudo)yum "Cannot find a valid baseurl for repo": CentOS 7 reached end of life, so use the vaulthttps://ohsudo.com/articles/yum-cannot-find-a-valid-baseurl-for-repo/https://ohsudo.com/articles/yum-cannot-find-a-valid-baseurl-for-repo/Fix yum "Cannot find a valid baseurl for repo: base/7/x86_64" and the CentOS 8 mirrorlist error: point the repositories at vault.centos.org, then plan a migration.Sat, 14 Nov 2026 00:00:00 GMTLinuxyumdnfcentosrepositorieseoltroubleshootingcontact@ohsudo.com (OhSudo)apt "dpkg was interrupted, you must manually run dpkg --configure -a": finish what was startedhttps://ohsudo.com/articles/dpkg-was-interrupted-configure-a/https://ohsudo.com/articles/dpkg-was-interrupted-configure-a/Fix apt "E: dpkg was interrupted, you must manually run sudo dpkg --configure -a": run it, then fix what stops it: a full disk, broken packages or a failing script.Tue, 10 Nov 2026 00:00:00 GMTLinuxaptdpkgubuntudebianpackagestroubleshootingcontact@ohsudo.com (OhSudo)apt "GPG error: NO_PUBKEY": add the key the right way, without apt-keyhttps://ohsudo.com/articles/apt-gpg-error-no-pubkey/https://ohsudo.com/articles/apt-gpg-error-no-pubkey/Fix apt "GPG error: The following signatures couldn't be verified: NO_PUBKEY": add the vendor's key to /etc/apt/keyrings with signed-by, and why apt-key is gone.Fri, 06 Nov 2026 00:00:00 GMTLinuxaptgpgubuntudebianrepositoriestroubleshootingcontact@ohsudo.com (OhSudo)apt "E: Unable to locate package": update, enable the component, or find its real namehttps://ohsudo.com/articles/e-unable-to-locate-package/https://ohsudo.com/articles/e-unable-to-locate-package/Fix apt "E: Unable to locate package": run apt update, enable universe or contrib, find the right package name, add the vendor's repository, and handle Docker images.Fri, 06 Nov 2026 00:00:00 GMTLinuxaptubuntudebianpackagesrepositoriestroubleshootingcontact@ohsudo.com (OhSudo)"error while loading shared libraries" and "GLIBC_2.xx not found": what the loader is telling youhttps://ohsudo.com/articles/error-while-loading-shared-libraries-glibc-not-found/https://ohsudo.com/articles/error-while-loading-shared-libraries-glibc-not-found/Fix Linux "error while loading shared libraries: cannot open shared object file" and "version GLIBC_2.xx not found": use ldd, install the library, run ldconfig, rebuild.Fri, 06 Nov 2026 00:00:00 GMTLinuxlddldconfigglibcshared-librariespackagestroubleshootingcontact@ohsudo.com (OhSudo)"umount: target is busy": find what holds the filesystem, and when umount -l is safehttps://ohsudo.com/articles/umount-target-is-busy/https://ohsudo.com/articles/umount-target-is-busy/Fix "umount: target is busy" on Linux: find the process with lsof or fuser, leave the folder, stop services, handle NFS and bind mounts, and know when umount -l is safe.Fri, 06 Nov 2026 00:00:00 GMTLinuxumountmountlsoffuserfilesystemstroubleshootingcontact@ohsudo.com (OhSudo)npm "EACCES: permission denied": fix it without sudohttps://ohsudo.com/articles/npm-eacces-permission-denied/https://ohsudo.com/articles/npm-eacces-permission-denied/Fix npm EACCES permission denied on global installs and in projects: use a version manager or your own prefix, repair root-owned files, and avoid sudo.Thu, 05 Nov 2026 00:00:00 GMTLinuxnpmnodejspermissionschowndockertroubleshootingcontact@ohsudo.com (OhSudo)"user is not in the sudoers file": how to get sudo back, even without the root passwordhttps://ohsudo.com/articles/user-is-not-in-the-sudoers-file/https://ohsudo.com/articles/user-is-not-in-the-sudoers-file/Fix "user is not in the sudoers file": add yourself to the sudo or wheel group with su, recover without a root password, use visudo safely and fix a broken sudoers file.Thu, 05 Nov 2026 00:00:00 GMTLinuxsudosudoersvisudopermissionsuserstroubleshootingcontact@ohsudo.com (OhSudo)SSH "Too many authentication failures": your agent offers too many keyshttps://ohsudo.com/articles/ssh-too-many-authentication-failures/https://ohsudo.com/articles/ssh-too-many-authentication-failures/Fix SSH "Received disconnect … Too many authentication failures": the agent offers every key before the right one. Use IdentitiesOnly and IdentityFile.Wed, 04 Nov 2026 00:00:00 GMTLinuxsshopensshkeysssh-agenttroubleshootingcontact@ohsudo.com (OhSudo)"Argument list too long": delete or move thousands of files on Linuxhttps://ohsudo.com/articles/argument-list-too-long/https://ohsudo.com/articles/argument-list-too-long/Fix "Argument list too long" for rm, mv, cp or grep with a wildcard: why the kernel refuses, and how find -delete, find -exec + and xargs handle any number of files.Mon, 02 Nov 2026 00:00:00 GMTLinuxbashfindxargsfilestroubleshootingcontact@ohsudo.com (OhSudo)"E: Could not get lock /var/lib/dpkg/lock-frontend": what is holding apt, and what to dohttps://ohsudo.com/articles/could-not-get-lock-dpkg-lock-frontend/https://ohsudo.com/articles/could-not-get-lock-dpkg-lock-frontend/Fix "Could not get lock /var/lib/dpkg/lock-frontend" on Ubuntu and Debian: find the process holding it, wait safely, and repair an interrupted dpkg.Mon, 02 Nov 2026 00:00:00 GMTLinuxaptdpkgubuntudebianpackagestroubleshootingcontact@ohsudo.com (OhSudo)Cron job not running? Find the reason in the log, PATH and environmenthttps://ohsudo.com/articles/cron-job-not-running/https://ohsudo.com/articles/cron-job-not-running/Fix a cron job that does not run or fails silently: check the log, PATH and environment, % signs, /etc/cron.d rules, permissions and lost output.Mon, 02 Nov 2026 00:00:00 GMTLinuxcroncrontabschedulingbashtroubleshootingcontact@ohsudo.com (OhSudo)"Job for nginx.service failed because the control process exited with error code": how to find the causehttps://ohsudo.com/articles/job-for-service-failed-control-process-exited/https://ohsudo.com/articles/job-for-service-failed-control-process-exited/Fix "Job for X.service failed because the control process exited with error code": read systemctl status and journalctl, test the config, and fix the usual causes.Mon, 02 Nov 2026 00:00:00 GMTLinuxsystemdsystemctljournalctlnginxservicestroubleshootingcontact@ohsudo.com (OhSudo)Linux process "Killed" with no error: find the OOM killer and stop it happening againhttps://ohsudo.com/articles/linux-process-killed-oom-killer/https://ohsudo.com/articles/linux-process-killed-oom-killer/A process that just prints "Killed" (exit code 137) was usually stopped by the Linux OOM killer. Find it in the kernel log, see what used the memory, and fix it.Mon, 02 Nov 2026 00:00:00 GMTLinuxoommemoryswapsystemddmesgtroubleshootingcontact@ohsudo.com (OhSudo)pip "error: externally-managed-environment": install Python packages the right wayhttps://ohsudo.com/articles/pip-error-externally-managed-environment/https://ohsudo.com/articles/pip-error-externally-managed-environment/Fix pip "externally-managed-environment" on Ubuntu 24.04 and Debian 12: use apt, a virtual environment or pipx, and know when --break-system-packages is acceptable.Mon, 02 Nov 2026 00:00:00 GMTLinuxpythonpipvenvpipxubuntudebiantroubleshootingcontact@ohsudo.com (OhSudo)"Read-only file system" on Linux: why the disk went read-only, and how to fix it safelyhttps://ohsudo.com/articles/read-only-file-system/https://ohsudo.com/articles/read-only-file-system/Fix "Read-only file system" errors: find the read-only mount, read dmesg to see why the kernel did it, then repair with fsck — and check whether the disk is failing.Mon, 02 Nov 2026 00:00:00 GMTLinuxfilesystemsext4fsckmountdmesgdiskstroubleshootingcontact@ohsudo.com (OhSudo)"sudo: unable to resolve host": fix /etc/hosts after a hostname changehttps://ohsudo.com/articles/sudo-unable-to-resolve-host/https://ohsudo.com/articles/sudo-unable-to-resolve-host/Fix "sudo: unable to resolve host … Name or service not known" on Ubuntu and Debian: add the hostname to /etc/hosts, and keep cloud-init from undoing it.Mon, 02 Nov 2026 00:00:00 GMTLinuxsudohostnameetc-hostscloud-initubuntutroubleshootingcontact@ohsudo.com (OhSudo)"Too many open files" on Linux: raise the right limit, or find the leakhttps://ohsudo.com/articles/too-many-open-files/https://ohsudo.com/articles/too-many-open-files/Fix "Too many open files" (EMFILE): check a process's real limit in /proc, raise LimitNOFILE for systemd services, and tell a low limit from a file descriptor leak.Mon, 02 Nov 2026 00:00:00 GMTLinuxulimitsystemdfile-descriptorsnginxnodejsjavatroubleshootingcontact@ohsudo.com (OhSudo)No space left on device: find what is filling your Linux diskhttps://ohsudo.com/articles/no-space-left-on-device/https://ohsudo.com/articles/no-space-left-on-device/Fix "No space left on device" on Linux: find the biggest directories and files, free space safely, and handle the cases where df says there is space.Sun, 01 Nov 2026 00:00:00 GMTLinuxdisk-spacedfdufindtroubleshootingcontact@ohsudo.com (OhSudo)"Permission denied" when running a script: 5 causes and fixeshttps://ohsudo.com/articles/permission-denied-running-script/https://ohsudo.com/articles/permission-denied-running-script/Fix "bash: ./script.sh: Permission denied" and "bad interpreter" on Linux: execute bits, noexec mounts, directory permissions, Windows line endings and shebangs.Sun, 01 Nov 2026 00:00:00 GMTLinuxbashpermissionschmodscriptstroubleshootingcontact@ohsudo.com (OhSudo)SSH "Permission denied (publickey)": how to find the real causehttps://ohsudo.com/articles/ssh-permission-denied-publickey/https://ohsudo.com/articles/ssh-permission-denied-publickey/Fix SSH "Permission denied (publickey)": read the server log, fix ~/.ssh permissions, check the key and sshd_config, and handle SELinux on RHEL.Sun, 01 Nov 2026 00:00:00 GMTLinuxsshopensshkeyspermissionstroubleshootingcontact@ohsudo.com (OhSudo)