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If a command or variable works in your terminal but fails in cron, the usual cause is that the scheduled job does not inherit your interactive shell’s full environment. Set the job’s command paths, required variables, and shell assumptions explicitly, then capture its output so you can see what failed.
Why cron cannot see what your terminal can
An interactive login shell may load startup files that define PATH, initialize a language version manager, export application settings, or create aliases. A scheduled cron job runs with an environment supplied by the cron implementation and the job’s owner; it is not necessarily the environment from your terminal.
POSIX specifies a baseline environment that includes HOME, LOGNAME, PATH, and SHELL, but actual behavior can vary by implementation. Its crontab description says the command field is executed by sh at the scheduled time. Cronie, for example, sets SHELL to /bin/sh and sets HOME and LOGNAME from the job owner’s passwd entry; its manual documents implementation-specific overrides and parsing. See the POSIX crontab specification and the Cronie crontab manual.
This explains two common symptoms: command not found usually means the executable is not in the job’s PATH, while an empty application setting usually means the variable was never set or exported for the process that needs it.
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Diagnose the job in a safe order
- Identify the scheduler, table, and owner. Confirm whether the machine uses Cronie, another cron implementation, a container scheduler, or a different scheduler. Check the crontab belonging to the account that runs the job. A personal crontab,
/etc/crontab, and files in/etc/cron.dare not interchangeable: system crontab formats commonly include a username field after the schedule, while a user crontab does not. Use the correct syntax for the actual table; Cronie documents its format and options in its manual. - Make failures visible. Temporarily append
>> /absolute/path/to/job.log 2>&1to the command, choosing a log path writable by the job’s account. Alternatively, configure mail or syslog output if those are available and monitored. Cronie documents mail delivery for job output and a daemon option for directing output to syslog in its cron manual. Logs can contain sensitive data, so restrict access and avoid dumping credentials. - Find the executable’s real path. In the terminal where the command works, run
command -v tool, replacingtoolwith the executable name. Use the resulting absolute path in the cron command, then verify that the cron account can execute the file and traverse its parent directories. If software is installed outside standard directories, add its location deliberately to the job’sPATH. - Set an intentional PATH. Cronie accepts environment assignment lines in a crontab. For example, a host might use
PATH=/usr/local/bin:/usr/bin:/bin, but check the actual directories and order for the target operating system and account. Do not put user-writable or otherwise untrusted directories inPATHfor privileged jobs. An absolute executable path is clearer for a single critical program; an explicitPATHis convenient when a job runs several commands. - Define application variables for the job. For a small number of static values, place assignments above the schedule line, such as
APP_ENV=production. To set a value only for one invocation, useAPP_ENV=production /absolute/path/to/program. In a wrapper that runs several commands, useexport APP_ENV=productionso child processes receive the variable. A shell variable that has not been exported is not automatically part of a child process’s environment; see Linux’s process environment documentation. - Make the shell requirement explicit. Cronie runs command fields through
/bin/shby default, or through the shell selected bySHELL. Bash-only syntax such as arrays or certain expansions will not work in a POSIX shell. If the job needs Bash, setSHELL=/bin/bashonly after confirming that Bash exists on the host. A wrapper script with a correct shebang is another clear way to select the interpreter. - Check crontab parsing and quoting. In Cronie, environment assignments are standalone active lines. A trailing comment on an assignment becomes part of its value, and comments cannot be appended to a command line. Quote values containing spaces as the shell requires. Cronie also treats an unescaped
%in the command field specially: text after it can be sent to the command’s standard input. Consult the Cronie crontab manual when a line parses differently than expected. - Test with a reduced environment. After preserving the intended account, permissions, and working directory, use
env -ito run a diagnostic command with only the variables you deliberately provide. This can expose reliance on a shell profile, but it does not reproduce every daemon detail. Compare the diagnostic output from cron with the environment in your terminal, and avoid recording secrets. - Remove temporary diagnostics. Keep only operational logging that is necessary, make log permissions appropriate for the data, and delete any environment dumps that may expose tokens, credentials, or internal paths.
Choose how to provide commands and variables
| Approach | Best fit | Trade-off |
|---|---|---|
| Absolute executable path | A single important program whose location is known | Makes command selection explicit, but every executable needs its own path. |
Explicit PATH |
A job that invokes multiple commands from known directories | More concise, but directory order affects which executable runs and unsafe directories can create risk. |
| Crontab assignments | A few static variables needed by one crontab’s jobs | Easy to see near the schedule, but offers limited setup and error handling. |
| Wrapper script | Jobs needing several exports, setup commands, a working directory, or explicit error handling | More auditable and flexible, but adds a file whose path, permissions, and shebang must be correct. |
| Cron or a service manager | Cron fits straightforward schedules; a service manager may suit tasks needing a managed environment, working directory, restart policy, or service lifecycle. | Availability and configuration depend on the host; systemd is not available everywhere. |
Example: a user crontab and wrapper
Adapt every path and variable to the target host. This is a user-crontab example; it does not include the username field used by common system crontab formats.
SHELL=/bin/sh
PATH=/usr/local/bin:/usr/bin:/bin
APP_ENV=production
*/5 * * * * /absolute/path/to/job.sh >> /absolute/path/to/job.log 2>&1If several values or setup steps belong in the wrapper, make them explicit there:
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#!/bin/sh
export APP_ENV=production
export PATH=/usr/local/bin:/usr/bin:/bin
exec /absolute/path/to/program --optionConfirm that the wrapper is executable by its cron owner and that all referenced paths exist. Paths shown here are examples, not universal defaults.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Version managers, aliases, and missing setup
Tools such as nvm and pyenv, as well as shell aliases, are often initialized in interactive startup files. Cron should not be assumed to read those files. Prefer a stable absolute path to the intended interpreter or executable. If initialization is required, call a deliberate setup script from a wrapper and verify that it works under the job’s shell and account.
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If the task fundamentally depends on a managed environment, a specific working directory, restart behavior, or service lifecycle, consider whether a service manager available on that host is a better fit than cron. Choose based on the host’s scheduler and operational needs rather than assuming a particular manager is installed.
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