try to replace path in second job and see if thats working, there seems to be no problem with the way it looks like
a cron log should be able to point if there is something else to look forward to.
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45 8 * * * /bin/df >> /oracle/SID/jm.txt 2>&1
45 9 * * * /bin/df >> /oracle/SID/sch_jobs/dt.txt 2>&1
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Thanks,
Kapil