889 commands · 48 cheat sheets · 6 subcategories

Linux master quick reference — Page 2

Browse 196 commands from 12 focused cheat sheets on page 2 of 4. Each example opens its matching detailed section.

Identity, Access, and Security · 15 commands

Linux sudoers Policy and Privilege Delegation Cheat Sheet

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List your privilegessudo -lView examples
List detailed privilegessudo -llView examples
Inspect another user's policysudo -U releasebot -llView examples
Validate the complete policysudo visudo --checkView examples
Parse one policy fragmentsudo visudo --check \ --file=/etc/sudoers.d/release-operatorsView examples
Safely edit a policy fragmentsudo visudo --file=/etc/sudoers.d/release-operatorsView examples
Define an operator aliasUser_Alias RELEASE_OPERATORS = %release-operatorsView examples
Define an exact command aliasCmnd_Alias API_STATUS = /usr/bin/systemctl --no-pager \ status api.serviceView examples
Grant a read-only service checkRELEASE_OPERATORS ALL = (root) API_STATUSView examples
Grant one noninteractive actionreleasebot ALL = (root) NOPASSWD: /usr/bin/systemctl \ restart api.serviceView examples
Invalidate your timestampsudo -kView examples
Set a controlled command pathDefaults:%release-operators \ secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"View examples
Enable I/O logging for a groupDefaults:%release-operators log_input,log_outputView examples
List recorded sessionssudo sudoreplay --listView examples
Test one exact authorizationsudo -U releasebot -l /usr/bin/systemctl restart \ api.serviceView examples

Identity, Access, and Security · 12 commands

Linux Users and Groups Cheat Sheet

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Inspect current identityidView examples
Inspect one userid -- deployView examples
Resolve a passwd entrygetent passwd deployView examples
Resolve a groupgetent group appopsView examples
Create a local groupsudo groupadd -- appopsView examples
Create a home-backed usersudo useradd --create-home --shell /bin/bash -- deployView examples
Set a password interactivelysudo passwd deployView examples
Append a supplementary groupsudo usermod --append --groups appops -- deployView examples
Inspect password agingsudo chage --list deployView examples
Lock password authenticationsudo usermod --lock -- deployView examples
Expire immediatelysudo usermod --expiredate 1 -- deployView examples
Delete after reviewsudo userdel --remove -- deployView examples

Identity, Access, and Security · 12 commands

OpenSSH Connections and File Transfer Cheat Sheet

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Connect to a hostssh deploy@example.comView examples
Use a non-default portssh -p 2222 deploy@example.comView examples
Use a host aliasssh productionView examples
Inspect effective configurationssh -G productionView examples
Show a public-key fingerprintssh-keygen -lf ~/.ssh/id_ed25519.pubView examples
Generate an Ed25519 keyssh-keygen -t ed25519 -a 64 -C 'deploy access'View examples
Load a key into the agentssh-add ~/.ssh/id_ed25519View examples
Forward a local portssh -N -L 127.0.0.1:15432:db.internal:5432 bastionView examples
Forward a remote portssh -N -R 127.0.0.1:18080:localhost:8080 serverView examples
Copy one filescp -- report.pdf deploy@example.com:/srv/reports/View examples
Open an SFTP sessionsftp deploy@example.comView examples
Trace connection setupssh -vvv productionView examples

Identity, Access, and Security · 20 commands

OpenSSL TLS and Certificate Inspection Cheat Sheet

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Show OpenSSL build detailsopenssl version -aView examples
Summarize a PEM certificateopenssl x509 -in server.crt -noout -subject -issuer \ -serial -datesView examples
Inspect critical extensionsopenssl x509 -in server.crt -noout -ext \ subjectAltName,keyUsage,extendedKeyUsage,basicConstraintsView examples
Compute a SHA-256 fingerprintopenssl x509 -in server.crt -noout -fingerprint -sha256View examples
Test the renewal windowopenssl x509 -in server.crt -noout -checkend 2592000View examples
Check a DNS identityopenssl x509 -in server.crt -noout -checkhost \ www.example.comView examples
Verify a server chainopenssl verify -purpose sslserver -CAfile roots.pem \ -untrusted intermediates.pem server.crtView examples
Verify chain and hostnameopenssl verify -purpose sslserver -verify_hostname \ www.example.com -CAfile roots.pem -untrusted \ intermediates.pem server.crtView examples
Verify a live TLS endpointopenssl s_client -connect www.example.com:443 \ -servername www.example.com -verify_hostname \ www.example.com -verify_return_error </dev/nullView examples
Show certificates sent by a serveropenssl s_client -connect www.example.com:443 \ -servername www.example.com -showcerts </dev/nullView examples
Require TLS 1.3openssl s_client -connect www.example.com:443 \ -servername www.example.com -tls1_3 -brief </dev/nullView examples
Inspect SMTP STARTTLSopenssl s_client -starttls smtp -connect \ mail.example.com:25 -servername mail.example.com \ -verify_hostname mail.example.com </dev/nullView examples
Request stapled OCSPopenssl s_client -connect www.example.com:443 \ -servername www.example.com -status </dev/nullView examples
Inspect and verify a CSRopenssl req -in request.csr -noout -text -verifyView examples
Check a private keyopenssl pkey -in server.key -check -nooutView examples
Extract a public keyopenssl pkey -in server.key -pubout -out \ server-public.pemView examples
Inspect PKCS#12 metadataopenssl pkcs12 -in identity.p12 -info -nooutView examples
Extract certificates onlyopenssl pkcs12 -in identity.p12 -nokeys -out \ certificates.pemView examples
Convert DER certificate to PEMopenssl x509 -inform DER -in server.der -outform PEM \ -out server.pemView examples
Extract certificate public keyopenssl x509 -in server.crt -pubkey -noout -out \ certificate-public.pemView examples

Identity, Access, and Security · 20 commands

SELinux Administration and Troubleshooting Cheat Sheet

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Read current modegetenforceView examples
Inspect SELinux statussestatusView examples
Show file contextsls -ldZ /srv/reporting /srv/reporting/index.htmlView examples
Show process domainsps -eZ | grep '[h]ttpd'View examples
Find recent denialssudo ausearch -m \ AVC,USER_AVC,SELINUX_ERR,USER_SELINUX_ERR -ts recentView examples
Analyze audit logsudo sealert -a /var/log/audit/audit.logView examples
Compare expected labelmatchpathcon -V /srv/reporting/index.htmlView examples
Add persistent mappingsudo semanage fcontext -a -t httpd_sys_content_t \ '/srv/reporting(/.*)?'View examples
Apply expected labelssudo restorecon -Rv /srv/reportingView examples
Remove local mappingsudo semanage fcontext -d '/srv/reporting(/.*)?'View examples
Inspect service booleansgetsebool -a | grep '^httpd_'View examples
Change boolean temporarilysudo setsebool httpd_can_network_connect onView examples
Persist a booleansudo setsebool -P httpd_can_network_connect onView examples
Inspect allowed portssudo semanage port -l | grep '^http_port_t'View examples
Authorize a custom portsudo semanage port -a -t http_port_t -p tcp 8443View examples
Set system permissive temporarilysudo setenforce 0View examples
Persist a permissive domainsudo semanage permissive -a httpd_tView examples
Re-enforce a domainsudo semanage permissive -d httpd_tView examples
Search allow rulessesearch -A -s httpd_t -t httpd_sys_content_t -c file -p \ readView examples
List policy modulessudo semodule -lfullView examples

Identity, Access, and Security · 20 commands

SSSD and Directory Integration Cheat Sheet

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Show SSSD versionsssd --versionView examples
List configured domainssssctl domain-listView examples
Check domain healthsudo sssctl domain-status --all example.comView examples
Validate configurationsudo sssctl config-checkView examples
Check secret-file permissionsstat -c '%a %U:%G %n' /etc/sssd/sssd.confView examples
Trace a user lookupsudo sssctl user-checks alice@example.comView examples
Resolve through NSSgetent passwd 'alice@example.com'View examples
Resolve groupsid 'alice@example.com'View examples
Evaluate access policysudo sssctl user-checks -a acct -s sshd \ 'alice@example.com'View examples
Discover a realmrealm discover example.comView examples
List realm configurationrealm listView examples
Join a realm interactivelysudo realm join --user=join-operator example.comView examples
Leave a realmsudo realm leave example.comView examples
List host principalssudo klist -k /etc/krb5.keytabView examples
Query LDAP discovery recordsdig +short SRV _ldap._tcp.example.comView examples
Query Kerberos recordsdig +short SRV _kerberos._tcp.example.comView examples
Expire one cached usersudo sss_cache --user 'alice@example.com'View examples
Expire one domain cachesudo sss_cache --domain example.comView examples
Read service logsjournalctl -u sssd.service --since '-15 minutes' \ --no-pagerView examples
Analyze recent requestssudo sssctl analyze request listView examples

Processes, Services, and System · 16 commands

Core Dumps, strace, and Linux Debugging Cheat Sheet

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List recent core dumpscoredumpctl list --since today --no-pagerView examples
Inspect one crashcoredumpctl info 4242 --no-pagerView examples
Filter by executablecoredumpctl list COREDUMP_EXE=/usr/local/bin/app \ --no-pagerView examples
Extract a core safelyumask 077; coredumpctl dump 4242 --output=app.coreView examples
Open latest matching dumpcoredumpctl debug /usr/local/bin/appView examples
Produce a batch backtracegdb --nx --batch --quiet -ex 'thread apply all bt full' \ /usr/local/bin/app app.coreView examples
Inspect core resource limitulimit -cView examples
Inspect kernel core handlersysctl kernel.core_patternView examples
Trace a new commandstrace -f -tt -T -s 256 -o trace.log -- \ /usr/local/bin/app --checkView examples
Trace file and network callsstrace -f -e trace=%file,%network -o trace.log -- \ /usr/local/bin/app --checkView examples
Attach to a processsudo strace -f -p 4242 -e trace=%file -o trace.logView examples
Summarize system callsstrace -f -c -- /usr/local/bin/app --checkView examples
Read a kernel stacksudo cat /proc/4242/stackView examples
Inspect process statuscat /proc/4242/statusView examples
Record mapped objectscat /proc/4242/mapsView examples
Read an ELF build IDreadelf -n /usr/local/bin/app | sed -n '/Build ID/p'View examples

Processes, Services, and System · 16 commands

Linux Boot and initramfs Diagnostics Cheat Sheet

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Show effective kernel argumentscat /proc/cmdlineView examples
Inspect boot loader statusbootctl statusView examples
Identify the running kerneluname -rView examples
List recorded bootsjournalctl --list-bootsView examples
Read previous boot errorsjournalctl --boot=-1 --priority=warning --no-pagerView examples
Read current kernel boot logjournalctl --dmesg --boot --no-pagerView examples
Summarize boot timesystemd-analyze timeView examples
Show critical chainsystemd-analyze critical-chainView examples
Rank unit activation timesystemd-analyze blameView examples
Inspect initrd dependenciessystemctl list-dependencies initrd.targetView examples
List a dracut imagelsinitrd /boot/initramfs-$(uname -r).imgView examples
List an initramfs-tools imagelsinitramfs /boot/initrd.img-$(uname -r)View examples
Print detected dracut argumentsdracut --print-cmdlineView examples
Inspect a newly built imagelsinitrd /tmp/initramfs-test.imgView examples
Boot to emergency targetsystemd.unit=emergency.targetView examples
Pause in dracut initramfsrd.break=pre-mountView examples

Processes, Services, and System · 14 commands

Linux Kernel Modules and sysctl Cheat Sheet

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Show running kerneluname -rView examples
List loaded moduleslsmodView examples
Inspect module metadatamodinfo e1000eView examples
Simulate module loadsudo modprobe --dry-run --verbose e1000eView examples
Load a modulesudo modprobe e1000eView examples
Remove a module safelysudo modprobe --remove e1000eView examples
Inspect effective modprobe configmodprobe --show-configView examples
List boot-load entriessystemd-analyze cat-config modules-load.dView examples
Read one sysctlsysctl vm.swappinessView examples
Change a runtime sysctlsudo sysctl -w vm.swappiness=10View examples
Check a staged sysctl filesystemd-analyze cat-config sysctl.dView examples
Apply system sysctl filessudo sysctl --systemView examples
Inspect kernel messagesjournalctl --dmesg --boot --no-pagerView examples
Read live module parametersfind /sys/module/e1000e/parameters -maxdepth 1 -type f \ -printView examples

Processes, Services, and System · 16 commands

Linux Package Management Cheat Sheet

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Search APT packagesapt search --names-only nginxView examples
Inspect APT metadataapt show nginxView examples
Search DNF packagesdnf search nginxView examples
Inspect DNF metadatadnf info nginxView examples
Refresh APT indexessudo apt updateView examples
Upgrade APT packagessudo apt upgradeView examples
Install with APTsudo apt install nginxView examples
Check DNF updatesdnf check-upgradeView examples
Upgrade with DNFsudo dnf upgradeView examples
Install with DNFsudo dnf install nginxView examples
Search Flatpak appsflatpak search org.gnome.TextEditorView examples
Install a Flatpak appflatpak install flathub org.gnome.TextEditorView examples
List package filesdpkg -L nginxView examples
Verify RPM filesrpm -V nginxView examples
Remove an APT packagesudo apt remove nginxView examples
Inspect DNF transactionsdnf history listView examples

Processes, Services, and System · 19 commands

Linux Processes Cheat Sheet

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List all processesps -efView examples
List your processesps -u "$USER" -o pid,ppid,stat,%cpu,%mem,commView examples
Inspect one PIDps -p 4242 -o pid,ppid,user,stat,lstart,cmdView examples
Show a process treeps -ef --forestView examples
Monitor processes livetopView examples
Find an exact namepgrep -a -x nginxView examples
Search full commandspgrep -a -u "$USER" -f "python3 -m http.server"View examples
Start a background jobpython3 -m http.server 8000 >server.log 2>&1 &View examples
Capture the latest PIDserver_pid=$!View examples
List shell jobsjobs -lView examples
Resume in foregroundfg %1View examples
Resume in backgroundbg %1View examples
Wait for a child processwait "$server_pid"View examples
Keep a command runningnohup python3 -m http.server 8000 >server.log 2>&1 &View examples
Request terminationkill -TERM 4242View examples
Force terminationkill -KILL 4242View examples
Signal an exact namepkill -TERM -x nginxView examples
Start with lower prioritynice -n 10 gzip archive.tarView examples
Change process priorityrenice -n 5 -p 4242View examples

Processes, Services, and System · 16 commands

Linux Time Synchronization and chrony Cheat Sheet

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Show synchronization statechronyc trackingView examples
List source selectionchronyc -n sources -vView examples
Show source statisticschronyc -n sourcestats -vView examples
Count source activitychronyc activityView examples
Wait for bounded accuracychronyc waitsync 60 0.01 0.1 10View examples
Explain source statechronyc selectdata -aView examples
Refresh source addressessudo chronyc refreshView examples
Mark sources onlinesudo chronyc onlineView examples
Collect measurements quicklysudo chronyc burst 4/4View examples
Step remaining correctionsudo chronyc makestepView examples
Print parsed configurationsudo chronyd -p -f /etc/chrony.confView examples
Configure an NTP poolpool time.example.net iburst maxsources 4View examples
Limit startup steppingmakestep 1.0 3View examples
Enable RTC synchronizationrtcsyncView examples
Read leap seconds from tzdataleapsectz right/UTCView examples
Persist NTS statentsdumpdir /var/lib/chronyView examples
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