Why does these sudo commands fail?

Question

I would like to add a crontab entry from a script as a normal user, so I use sudo to get root permissions, but fails no matter what I try.

$ sudo { crontab -u root -l; echo ' 15  9  *  *  * root /opt/script.sh'; } | crontab -u root
bash: syntax error near unexpected token `}'

$ sudo echo ' 15  9  *  *  * root /opt/script.sh' >> /etc/crontab
bash: /etc/crontab: Permission denied
$ sudo echo ok
ok

score 6 · Answer 1 · answered Nov 19 '13 at 17:04

6

Because you are running

sudo echo .......

as "su" then writing the result to /etc/crontab with:

>> /etc/crontab

so in the moment you are writing to /etc/crontab you're not "su" anymore

answered Nov 19 '13 at 17:04

kappa

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How would you go around this? – Sandra Schlichting Nov 19 '13 at 17:07
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"sudo crontab -e" is the preferred way to do it – kappa Nov 19 '13 at 17:08
@hek2mgl the command after pipe is still not executed as su – kappa Nov 19 '13 at 17:10
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@SandraSchlichting Or invoke an new shell `sudo bash -c "echo \"hello\" >> file"` – user000001 Nov 19 '13 at 17:11
@hek2mgl I don't understand the example. I haven't used `tee` before. Can you give a full example? – Sandra Schlichting Nov 19 '13 at 17:15
@kappa Thanks, I frequently forget this... :) (at) Sandra have no better example, it was just wrong.. sorry – hek2mgl Nov 19 '13 at 17:15

score 1 · Accepted Answer · answered Nov 19 '13 at 17:20

1

In sudo echo ' 15 9 * * * root /opt/script.sh' >> /etc/crontab, sudo echo ' 15 9 * * * root /opt/script.sh' is ran first then the shell takes the output of the sudo command and appends it to /etc/crontab. Since the shell is started as a normal user and so doesn't have root privileges, the shell can't write to /etc/crontab, which only root can modify. To solve the problem one starts a subshell as root, which allows it to append to /etc/crontab. Fortunately, this has already been implemented as su -c, however since the system uses sudo, sudo has to be prepended. The fixed command is sudo sh -c "echo ' 15 9 * * * root /opt/script.sh' >> /etc/crontab"

answered Nov 19 '13 at 17:20

Ramchandra Apte

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I thought the question was "Why does these sudo commands fail?" , while this answer is to the question "How can i put a line in crontab with sudo?" or "how can i run a shell command in sudo" – kappa Nov 20 '13 at 09:06
@kappa `"echo ' 15 9 * * * root /opt/script.sh' >> /etc/crontab` can be replaced with any other shell command. – Ramchandra Apte Nov 20 '13 at 09:24
sudo sh -c can be replaced by sudo -s. – petertc Oct 27 '14 at 03:37

Why does these sudo commands fail?

2 Answers2